SCAPHULA. 131 



unica lata, planulata, aliquaudo obsoleta, a natibus ad marginem 

 decurrente, munita, iiitus cajnilescens, autice rotiindata, postice 

 oblique truncata, margine ventrali aiitice convexa, postice vix 

 concaviuscula (testae j unions recta). Carina perelevata, acuta, 

 valvas in paginas duas dividens, autica tumida, postica concava. 

 Area nitida, sub lente striatula, ligamento rliombeo solum antice 

 indata. Dentes cardinales postici breves, obliqui, ab extremitate 

 I'eniotiusculi. 



1. 2. 



Long 3-5 3 mm. 



Lat 10 8 mm. 



Diam 6*5 5 mm. 



Hah. Irawady River at Pegu ; found " under stones in creeks, 

 adhering by a byssus " ; Mahanadi River, at a point five miles 

 above Hambalpur, Orissa (Chaudhuri). 



The autlior appends the following notes to his description : — 

 " Shell very tumid, elongately rhomboidal (the ventral and dorsal 

 margins being parallel as in /S. celox)^ covered with a thick dark 

 epidermis, which is rather rough and radiately ribbed behind the 

 keel. Beneath the epidermis the shell is white, and decussately 

 very minutely sculptured, one flat broad rib, scarcel}'' raised, and 

 occasionally obsolete in old specimens, passing from the umbones 

 to the n)argin just in front of the keel. This is scarcely dis- 

 tinguishable until the epidermis is removed. The valves are bluish 

 within, rounded in front, obliquely truncated at the posterior 

 margin ; the ventral margin is convex anteriorly, subcoucave 

 posteriorly, being straight for the greater part of its course in 

 young shells, but becoming sliglitly concave, at the spot where the 

 byssus passes out, in old specimens. The keel is verj' high and 

 sharp, separating the valves into two subdivisions, the anterior of 

 which is tumid, the posterior concave. The area is polished and 

 striated rather obliquely, the ligament diamond-shaped and 

 <,'Over;ng only the anterior portion, about ly to | the length of the 

 area. The hinge teeth are oblique, but less so than in either 

 8. celox or S. jyinna, and the posterior teeth are much farther from 

 the extremity of the shell than in either of those species." 



''The great distinction between this species and the other two 

 previously described is in the far greater tumidity of the valves, 

 which are nearly twice at broad in their diameter from side to side 

 (of the closed valves) as they c.re from the dorsal to the ventral 

 margin. The proportion of the two diameters in the present 

 species averages about 12 : 7. In -6'. celox it is 12 : 10k and in 



k2 



