CHASMOCARCINUS ROBERTS!, A NEW CRAB SPECIES FROM THE MIOCENE OF VIRGINIA, WITH NOTES ON THE GENUS FALCONOPLAX (CRUSTACEA, DECAPODA, GONEPLACIDAE) WARREN C. BLOW NATIONAL MUSEUM OF NATURAL HISTORY SMITHSONIAN INSTITUTION, WASHINGTON, D.C. and RICHARD H. BAILEY DEPARTMENT OF GEOLOGY NORTHEASTERN UNIVERSITY BOSTON, MASSACHUSETTS ABSTRACT studies by providing him with additional The new species Chasmocarcinus crab material until his retirement in 1973. robertsi from the upper Miocene Eastover Poor health prevented Roberts from com­ Formation of Virginia is described and pleting a number of his projects including compared to other closely allied living and the description of this new species of Fal­ fossil representatives of this genus. The conoplax. Upon his retirement Roberts comparative morphology of fossil and liv­ handed over that job to the senior·author. ing species demonstrates that the fossil genus Falconoplax Van Straelen, 1933, is a Family GONEPLACIDAE MacLeay, 1838 junior subjective synonym of Chasmocar­ Subfamily CHASMOCARCININAE cinus Rathbun, 1898. Chasmocarcinus Serene, 1964 robertsi occurs in, or was derived from, Genus CHASMOCARCINUS Rathbun, 1898 Miocene strata, not "?Paleocene beds" as reported by previous authors. Specimens Chasmocarcinus RATHBUN, 1898a: 284. of C. robertsi found near Little Cove Point, Type species, by indication, Chasmocarcinus typicus Rathbun, 1898. Maryland represent the northernmost known occurrence of living or fossil Chas­ Falconoplax VAN STRAELEN, 1933: 11. mocarci nus. Type species, by monotypy, Falconoplax kug­ leri Van Straelen, 1933. INTRODUCTION Definition (Modified from Rathbun, 1898a): Carapace thick, broadest posteriorly, tapering In 1961 Lauck W. Ward discovered a anteriorly, with lateral margins forming a curve small fossil crab about 43 km northeast of continuous with the anterior margin. Front nar­ Richmond along the south bank of the Mat­ row, bilobed. Orbits marginal, oblong. Ptery­ taponi River, in King William County, Vir­ gostomian region with horizontal suture. Anten­ ginia. Subsequent field work by Ward in nula with basal joint very large and hemispheri­ this and other nearby areas along the river cal. Epistome nearly perpendicular, projecting produced more specimens which, in 1963, below maxillipeds. Maxillipeds widely gaping, parallel, longitudinally placed; merus suboval, he sent to the National Museum of Natural palpus articulating at antero-internal angle. Ab­ History in Washington for identification. domen much narrower at base than sternum; Henry B. Roberts of the museum ex­ third, fourth, and fifth segments coalesced in amined these crabs and concluded that male. Sternite 8 with genital groove covered they represented a new species of the with supplementary accessory plate. Abdominal genus Falconoplax, which at that time was segments distinct in female. Chelipeds with known only from the type species, F. kug­ merus trigonal, carpus quadrate, manus short leri Van Straelen, 1933, a crab described and broad, fingers long and slender. Ambulat­ ory legs slender, subcylindrical, third pair the from and restricted to the Eocene of Fal­ longest, second next, fourth the shortest. Dac­ con, Venezuela. In 1964 we began our field tylus of last pair recurved. studies of the fauna associated with the The following characters should be added to crab-bearing lag deposits along the Matta­ Rathbun's (1898a) description of the type species poni River, and supported Roberts's of Chasmocarcinus: anterior dorsolateral mar- EDITORIAL COMMITTEE FOR THIS PAPER: BARBARA A. BEDETTE, U.S. National Museum, Washington, D.C. RAYMOND B. MANNING, U.S. National Museum, Washington, D.C. THOMAS R. WALLER, U.S. National Museum, Washington, D.C. 175 176 Tulane Studies in Geology and Paleontology Vol. 25 gin with persistent, minute tooth above promi­ ly Dorippidae, subfamily Tymolinae. His nent, V-shaped lateral groove formed by inter­ justification for this move was based on, secting post-subhepatic and cervical grooves. among other characters, the presence of a These two characters are also present on the wide sternal plate "with deep sternal type species of Falconoplax. grooves leading medially from 5th pereio­ pod coxae of female." These grooves are Included Recent and fossil species: apparently those formed on internal molds Recent species and their type localities - by the dissolution of the exoskeleton, and C. typicus Rathbun, 1898a:285 (North of are very misleading. Collins and Morris Trinidad); C. obliquus Rathbun, 1898a:286 (1976) followed Glaessner in placing Fal­ (Bahamas, SE of Andros Isl., in Tongue of conoplax in the Tymolidae when they Ocean); C. latipes Rathbun, 1898b:602 named a second species, F. bicarinella, (Mexico, Magdalena Bay); C. cylindricus from the Eocene of Barbados. In this Rathbun, 1901:10 (Puerto Rico, Mayaguez paper they mentioned a third "unde­ Harbor); C. rathbuni Bouvier, 1917:391 scribed species from the ?Paleocene of (Brazil, Rio Grande do Sul); C. superbus Virginia, U.S.A." Glaessner (1980), citing (Boone, 1927:16), (Belize, Glover Reef); C. the criteria used by Guinot (1977,1978), mississippiensis Rathbun, 1931:72 (Missis­ stated that "it would seem necessary to ex­ sippi, Mississippi Sound near Horn Island); clude this genus" (Falconoplax) from the C. longipes Garth, 1940:90 (Panama, Secas Tymolidae. Bailey and Blow (1987), in an Ids. and Colombia, Port Utria); C. abstract and without elaboration, referred panamensis Serene, 1964b:258 (Bay of to Falconoplax as a junior synonym of Panama, Isl. del Rey); C. chacei Felder Chasmocarcinus, a genus in the family and Rabalais, 1986:548 (northwestern Gulf Goneplacidae. Glaessner and Secretan of Mexico, vicinity of Flower Garden (1987) discussed and figured the genital Banks). groove present on the eighth sternite of Fossil species, their type localities and Falconoplax, and retained this genus in the age -C. kugleri (Van Straelen, 1933:11), Tymolidae. Tavares (1992) removed Fal­ (Venezuela, central Falcon; Eocene); ?C. conoplax from the Cyclodorippidae ( = bicarinella (Collins and Morris, 1976:109), Tymolidae) and, based on the "character­ (Barbados, Spa; Eocene), type not ex­ istics of its thoracic sternum," stated that amined. The presence of two small blunt Falconoplax is related to the Gonep­ spines bordering the cervical notch men­ lacidae. In this paper we repeat and ex­ tioned by Collins and Morris and the strong plain our earlier position that Falconoplax diagonal dorsal ridges seen in their figure is a synonym of Chasmocarcinus and of the holotype suggest that this species therefore a member of the Goneplacidae. does not belong here; C. seymourensis Feldmann and Zinsmeister, 1984: 1056 The relationship of Falconoplax to Chas­ (Seymour Island, Antarctica; Eocene). mocarcinus was called to our attention by a Remarks: The similarities between Fal­ specimen label in the U.S. National Muse­ conoplax and Chasmocarcinus have, sur­ um collections corrected by the late Mary prisingly, not been noted by previous au­ J. Rathbun to read: "Chasmocarcinus kug­ thors. With the exception of a new species leri, Van Straelen, 1933." introduced by Collins and Morris in 1976, With Rathbun's label in mind we ex­ Falconoplax has received little attention on amined Van Straelen's types of F. kugleri the generic level. However it has received in 1985 and compared them to the types of considerable attention on the family level. C. typicus. Both species share generic A brief review of the literature dealing characteristics and are remarkably similar with this genus and its family placement except for size. Falconoplax kugleri is, on follows. the average, considerably larger than C. Van Straelen (1933) erected the genus typicus and most other living representa­ Falconoplax to accommodate his new fossil tives of Chasmocarcinus. However, at least species F. kugleri, from the Eocene of Ven­ one living species, C. latipes Rathbun, ezuela, and placed it in the family Gonep­ 1898, does approach the large size attained lacidae without explanation. Glaessner by fossil forms. Size, therefore, does not (1969) transferred Falconoplax to the fami- appear to be of generic importance here. No. 4 New Virginia Miocene Crab 177 Unfortunately, Van Straelen based his CHASMOCARCINUS ROBERTS!, n. sp. description of F. kugleri on about 200 inter­ Plate 1, figures 3-5; nal molds of carapaces. Even the figured Plate 2, figures 3-12. type is completely lacking the exoskeleton. Such internal molds are misleading in the An undescribed species from the ?Paleocene of Virginia, U.S.A. COLLINS and MORRIS shape and surface features they present. 1976, p. 112; TAVARES, 1992, p. 73. ' For example, the figured type of F. kugleri Diagnosis: Carapace large, thick, subquad­ shows a narrow front with wide orbits. Ex­ rate in dorsal outline; anterior dorsolateraljunc­ terior exoskeleton impressions of these tion with granulated ridge; dorsal and ventral same features on some paratypes show surfaces coarsely punctate; fingers of male their proportions to be nearly the reverse, major chela very long, slender, greatly de­ or more like those of Chasmocarcinus. flected, proximal end of propodus with row of Similarly the tubercles, diagonal ridges, five distinct teeth, first and fifth prominent; car­ and other features described by Van pus in both sexes with stout curved spine on Straelen (1933) for F. kugleri and used in inner angle; eighth sternite of male with genital part by Collins and Morris (1976) to assign groove covered by accessory plate. F. bicarinella to Falconoplax