24 NILS HJ. ODHNER, STUDIES ON RECENT CHAMIDAE. 



4. Morphology of Pseiidocliama pusilla n. sp. 



Figs. 20—27. 



Shell small-sized, ventricose, with somewhat irregularly orbicular outline, slightl}' 

 inequivalve, attached by the foremost third of the right valve. Lovver (right) valve 

 only a little more inflated than the upper one but with the umbones produced higher. 

 Umbones only feebly spiral. Dissoconch rounded square with a few distant con- 

 centric threads and traces of some radiating posterior riblets (fig. 21). Sculpture 

 of both valves consisting of radiating rows of small blunt spines more or less openly 

 furrow-shaped on their under sides; some ones on the hinder part of the shell more 

 dilated, squamous. Colour of the exteriör pale-rosc. Interiör of the shell bright 

 rose, lighter at the margins; these crenelated near the edge all round. Pallial line 

 simple without sinus; mnscular scars distinct, the anterior one produced somewhat 

 higher and narrower, the posterior shorter and broader. Ligament short, superficial, 

 its posterior end penetrating to half the-breadth of the dental plate. Hinge with 

 distinct elements: in the right valve (fig. 20 b, Ii) two conical teeth (1 and 3 b) rising 

 behind the mnscular impression close to each other, separated only by a deep and 

 narrow hole, with feebly bifid apices and some irregular grooves on their umbonal 

 and inner sides. Behind the teeth a large furrow-shaped dental socket and behind 

 it, just below the ligament, a row of tubercles representing a rear cardinal (5 b), 

 extending to the end of the ligamental groove and followed there by an indistinct 

 tubercular lateral tooth (L I). In the left valve (fig. 20 c,e,g): close above the 

 adductor scar a deep dental hole, bounded at the posterior side by a narrow tri- 

 angulär tooth (2 b) with some lateral grooves; in front of it, above the dental socket, 

 a row of tubercles indicating a vestigial anterior cardinal (2 a). Behind the median 

 tooth a deep obliquely triangulär pit and behind it a crest-like tooth (4 b) rifled on 

 its upper side and extended, parallel to the shell margin, to the end of the liga- 

 mental groove. Behind the ligament an indistinct lateral (LP II) fitting out of 

 LP I, and inside it, separated by a socket, a marginal tooth (M), 1 fitting inside 

 LP I. No scars of the branchial suspensor muscle were seen. 



Dimensions in millimetres : height of the closed shell 7.3, of the left valve 6; 

 length (in antero-posterior direction) 6.3; thickness (breadth) of the closed shell 5.3, 

 of the left valve 2.1. 



Locality: 4 specimens of this new species collected in the Strait of Macassar 

 are preserved in the collections of the Swedish State Museum acquired from Salmin 

 ( 29 /v 1877). 



In all probability, to judge from the organization of the soft parts (see below), 

 this species is identical with a small form obtained by the Siboga Expedition in St. 

 79 a (Strait of Macassar, Borneo bank 2° 38'.s S, 117° 46' E, 54 m, fine coral-sand), 



1 Cf. Odhner 1918 and above. 



