OP SOUTHEEN INDIA. 381 



below tlie beaks. On the wliole, this ornamentation resembles that of Septifer, 

 but there is no trace of an internal lamella in the Indian fossil. It diflPers from 

 Mod, Cuvieri (Myt, Uneatus apud d'Orbigny) by its curyed or twisted shape. 



Locality, — Vylapaudy, in a whitish sandstone. 



Formation, — Arrialoor group. 



MYTILTJS, Linne, 1758, (see p. 371). 



1. Mytilijs Arrialgoiiensis, Stoliczka, PI. XXIII, Pigs. 2, 3, 5. 



Myt, testa elongato sub-tetragona, umhonibus attenuatis, sub-actitis, terminalibus 

 instructa, compressiuscula ; area ligamentali sub-recta^ in marginem dorsalem lente 

 curvatum inconspicue transeunte, marg, ventrali paulo insinuato, postico sub- 

 rotundato ; regione ventrali angustissima, fere verticaliter declivi; superficie striis 

 incrementi tenuibus et nonnullis sulcls crassioribus notata, 



A small rather compressed species of a sub -quadrangular shape, with pro- 

 minent, attenuated terminal beaks, slightly varying in height, the posterior dorsal 

 edge being a little more extended and curved in the flatter specimens, while in 

 the slightly more tumid ones it is almost straight. The surface only exhibits 

 fine concentric striae, these being occasionally intersected by stronger marked 

 depressions of growth. 



Locality. — ComarapoUiam, in a whitish sandstone ; not common. 



Formation, — Arrialoor group. 



XXXIX. Family,— FINNIDJE, 



The animals of Finna have the mantle-margins entirely disunited, one pair 

 of long gills and one of moderately elongated triangular palps on each side, the 

 former originating between the palps ; the foot is short, conical, grooved below, 

 and with a strong byssal gland; the pedal muscles are well developed, divided into 

 three pairs, one anterior, one median, and one posterior, the two latter consisting of 

 several more or less isolated branches ; the posterior adductor is semi-oval or 

 roundish, the anterior much smaller, but well marked ; the anus is situated on a 

 prolongation of the rectum, possessing at the side peculiarly elongated valvulse, the 

 nature of which is as yet unknown. 



Shell sub-triangular, equivalve or sub-equivalve, pointed at the beaks, gaping 

 posteriorly, hinge toothless, ligament linear, long, almost internal ; muscular scars 

 unequal, the anterior situated at the beak, posterior sub-central, ovate or roundish ; 

 pallial impression entire ; outer layer of shell fibrous, inner within the pallial line 

 more or less distinctly perlaceous. 



The genera to be placed in this family are Aviculopinna, TricMtes, Finna, and 

 Bryophila, The two former are known only fossil, the two others recent. A few 

 species of Finna have been recorded from palaeozoic rocks, but the forms are 

 somewhat aberrant and may belong to distinct types. True species of Finna 



