UNIO MISOOI.ENSIS. 259

NOTE XXXVI.

Description of a new species of Unio

BY

M.M. Schepman

Unio misoolensis, n. sp.

Shell rather elongated, compressed, very inaequilateral,

at the umbones laying about one sixth of the whole length of the shell, rather smooth, with numerous fine concentric striae; umbones little prominent, decorticated in the adult,

half shells in grown with conspicuous radiating folds,

more or less over the disk extending of the shell; moreover

few the a radiating grooves occupy anterior part of the and shell, microscopic radiating wrinkles of the epidermis

cover the posterior slope; epidermis reddish-brown in the

adult, yellowish olive-green in the young ones. Upper

margin slightly curved, anterior margin rounded, slightly

protruded below; ventral margin incurved, posterior margin

with the forming upper one a more or less obtuse angle,

Notes from the Leyden Museum, Vol. XVIII. 260 UNIO MISOOLENSIS.

regularly curved above, rounded below and running with

the umbonal which is rather a very obtuse angle at ridge, obtuse, into the ventral margin. long, narrow,

yellowish-brown.

Nacre bluish white, more iridescent near the posterior

than part, brownish near the umbones; scarcely more one

in short, thick, crenated tooth each ; a small knob in the left valve be considered as a second may perhaps tooth; lateral lamellae: 2 in the left valve, one in the right

are curved, rather thick. one; they elongated, slightly

rounded Anterior scars: a large one, which is rather

and below the deep, a much smaller, very deep one, just

line distinct. tooth; posterior scars very shallow; pallial

anterior ventral much thickened near the part of margin, forming a callus, which is connected with another

umbones callus, running from the to this ventral one.

16 Long 65, alt. near the umbones 24, diam. mill.

Locality. Misool (Hoedt). — In the collection of the

Leyden Museum.

of this Unio the known The nearest ally , amongst spe-

be Unio cies of the same geographical region, may Bec-

carianus Canefri, or its variety a but it differs in Tapp. , shape and ; the anterior margin in that species is not protruded below, the posterior part is much more

and acuminated in Beccarianus and the line elongated , from the ligament to the posterior end is much straighter, while it is curved in the new species.

Rhoon near Rotterdam, February 1897.

Notes from the Leyden Museum, "Vol, XVIII.