1867.] Contributions to Indian Malacology. 67 



Class CONCHIFERA. 



Family PHOLADID^E. 



No. 28, Martesia fiuminaHs, n. sp. PI. Ill, fig. 1, 2, 3. 



Testa ovata-conica, valde incsquilateralis, antice hemispherica, postice 

 sensim acuminata, extremitate membranacea, albidd, tenuis. Valvce 

 versus margines epidermide crassd, coriaced indictee, pagina antica jux- 

 ta cardinem coshdis confertissimis, sinuatis, concentricis, lineisque 

 radiatis elevatis decussantibus pxdclire ornata, subtus glabra, postica 

 concentrice striata. Galium trilobato-peltatum, medio divisum. Valvula 

 dorsalis rudimentaria, cornea. 



Lat. 12J, long. Q, alt. h\ mill. 



Shell ovately conical, white, thin, inequilateral, anterior extremity 

 hemispherical, posterior regularly acuminate and membranaceous at 

 the extreme end. Valves near the edges covered with a thick coriace- 

 ous epidermis, which in places, and especially towards the posterior 

 extremity, extends beyond the margin and forms a membranaceous 

 fringe, uniting the valves more or less. Each valve is divided into two 

 parts by a line passing obliquely from the hinge to the ventral margin 

 and inclined slightly backwards ; in front of this line the shell near 

 the hinge is decussated with very close sinuate concentric and subdistant 

 radiating costulation ; near the ventral margin it is smooth. Behind 

 the oblique line the valves are concentrically striated, more or less in- 

 distinctly. The callus covering the hinges is trilobate and divided by 

 a fissure in the centre ; dorsal valve rudimentary, horny, commencing 

 at some distance from the hinge, increasing in breadth backwards, but 

 very narrow throughout. 



This species appears most nearly allied to M. rivicola, Sow., which 

 was found perforating floating logs in a river in Borneo. The pre- 

 sent species is blunter and shorter, and M. rivicola is destitute of the 

 sculpture on the anterior portion of the valves. 



M. fluminalis was found boring in soft argillaceous sandstone, in 

 creeks far from the sea, where the water was brackish. The external 

 orifice in the stone is very minute, and must have been made by the 

 shell when very young. Inside, the burrow exactly fits the shell, so that 

 the only possible motion is rotation upon the longest axis of the shell. 



The epidermis appears normally to cover the posterior subdivisio 

 of: the valves, but it is always deficient, except towards the margins. 



