OP SOUTHERN INDIA. 383 



scar very large, sub-central ; structure of shell fibrous and variously ornamented on 

 the surface, internally pearly within the extent of the pallial line, which is entire ; 

 type, P. fiobilis, Linne. The valves are often split along the median line, which 

 seems to have been more commonly the case in fossil species of the genus, than 

 it is met with in recent shells. The anterior adductor sometimes forms concentric 

 lamellse in the beaks, their outer surface becoming eroded, and sometimes replaced 

 by a regular chambered vault. This was noted as indicating probably a generic distinc- 

 tion in some fossil species, but is certainly only the result of regular growth and may 

 be often observed also in recent specimens. Species of Finna are rare in palaeozoic 

 rocks ; they sensibly increase during the Jurassic and cretaceous period, become 

 again apparently less numerous in the tertiary epoch, and attain their maximum of 

 development in the present tropical regions, only very few being known from 

 northern seas. 



The name Atrina has been proposed for P. saccata, Linne, which is of a pecu- 

 liar vitreous structure, and has entire beaks. It barely marks a distinct sub-genus, 

 and it certainly cannot be used to the extent accorded to it by H. and A. Adams. 



4. Bryophila, Carp., 1864, (Ann. and Mag. Nat. Hist., 3rd ser., xiii, p. 314). 

 Shell like a minute Finna, with pointed beaks ; upper margin straight, with a strong 

 internal ligament, anteriorly at the byssal sinus somewhat insinuated, ventrally and 

 posteriorly rounded and gaping; posterior muscular scar sub-central, indistinct; type, 

 B, setosa, Carp., from Cape St. Lucas, found between algse. The animal is stated 

 to be viviparous, and in form '' like minute Finna, or a transverse Ma7^garitop}iora 

 without ears, or an Isognomon f=Melina=FernaJ without pits." Its length is only 

 0*13 inch and the width 0'2 inch, but it is said to be adult. The structure of the 

 shell agrees with that of Finna, being fibrous externally, nacreous internally. 



List of cuetaceous species. 



1. TricUtes Ficteti, Camp., (Mat. p. 1. Pal. Suisse, vme ser.^ 4™® part., 1869, p, IQ, is 

 the only^ well known cretaceous species. 



Pinna, see Pictet and Camp., Pal. Suisse, ivme ser., 3"^® part., p. 536. 



2-24. — P. sulcifera, Leym., Gillieroni, helvetica, and Homhresi, Pict. and Camp., JRohinaldina, 

 d''Orb., gracilis, Phil., crassa, Sow., (^myitis, P. and C, sub-tetrayona, d''Orb., hicarinata,-\ Math., 

 Moreana, Galliennei, Neptuni, and Ligeriensis, d''Orb., sulcata, Woodw., recticostata, d^Orb., 

 petasunculus , Math., Moulinsii, d''Orb., Cott(2, Gein., cretacea, Schloth., quadr angular is , Goldf., 

 fenestrata, Rcem., nodulosa, Reuss. 



25-28. — P. ahrupta, sub-lanceolata, suh-cuneata, and fiigax are described by Eichwald from 

 various parts of Russia ; the three first named species are said to be from Neocomien, the last from 

 Cenomanien deposits, (Leth. Ross., x livr., 1867, p. 545 et seq.). 



29-33. — P. calamitoides , Shum., fibrosa, Meek and H., laqueata, Con., rostriform.is , Mort.^ 

 and lingula, Newb., are noticed from North America by Meek in Smith. Misc. Coll., No. 177, 

 1864, p. 9. 



* Pinnigena magna, d'Orb., Prod. II, p. 107, is quite insufficiently characterized. It is quoted from Neocomien beds, 

 t Zittel unites this species with cretacea, which appears to me very probably correct (Denksch. Akad., Wien, xxv, pt. ii, 

 p. 87), and makes some very valuable observations regarding allied species and synonyms. 



5 A 



