354 CllETACEOUS PELECYPODA 



4. TiiiGONOABCA Gamana, Fovles, PL XX, Figs. 4-5, and PI. L, Fig. 7. 



18'IG. Arm Gamana, Forb., Trans. Geol. Soc, LoncL, vii, p. 148, pi. xvi, fig. i—eadem aucloruin. 

 1847. Ai: similis, d'Orb., Voy. Astrolabe, pi. iv, figs. 33-34. 



Triy. testa oblique trcqicsoidea, injlata, crassa, sub-incequivalvi, antlce sensim 

 angiiste suh-rotunclata, postice valde carmata et producta, declivitate postica abmpiu, 

 ad marginem oblique truncata ; superficie concentrice minute striata, striis confertis, 

 sulcis profmdioribus intersectis, parte postica scepe coslulis radiantibus nonuullis sub- 

 obsoletis notata ; area ligamentali lata, crasse lamellose furcata ; cardine dentibus 

 loiKjioribus, obliqiiis, 5-6 iti utroque latere, in margine cardinali recto 20-26, ad 

 medium midto brevioribus, instructo ; impressione musculari postica in lamina modice 

 elevata sita. 



Height of shell : its length ... ... ... 0-76 - 0-80 



Thickness „ : „ ... •■• ■.• 070 - 072 



This species appears closely allied to Trig. Trickinopolitensis, difFeriug from 

 it bv a more solid structm-e of the shell, which also is more inflated ; it possesses a 

 Avid'cr ligamental area, and has the anterior part conspicuously narrowed ; the 

 radiating sti-iee are either very faint or more often quite obsolete. Of European 

 species Zittel's Trlgon. crassitesta is closely allied, but apparently shorter and 



higher. 



Localities.— 'PooAoQV, Odium, Mouglepaudy, &c., mostly in a brownish calca- 

 reous sandstone ; not uncommon, 



Formalion.—Ootatoov group. 



5. Trigonoarca Brahminica, Forbes, PI. XVIII, Fig. 13, and PI. XX, 



Figs. 1 and 3. 



1846. Area hrahminira, Forbes, Trans. Geol. Soc, Lond., vii, p. 149, pi. xvi, fig. l—eadem auctorum. 



1847. Area Foiitaideri, d'Orb., Voy. Astrolabe, Paleont, pi. v, figs. 34-35. 



Trig, testa sub-quadra ngulari, injlata, antice Icviter rotundata, p)Ostice plus 

 minusve producta atque oblique truncata, area in speciminibus junioribus sub-ai/gusta, 

 in adultis latissima ; superficie striis concentricis crassiusculis, filifoi'mibus, confer- 

 tissimis et alteris radiantibus minutissimis, medio fere omnino obsoletis, induta. 



Height of shell : its length ... ... ... 074-0-80 



Thickness „ : „ ... ... ... 0-68 - 0-90 



Tlie peculiar character of this species consists in the regularity of the con- 

 centric filiform and very close striation, being quite distinct from that of any other 

 of the Indian species. There are also some very fine radiating striae to be noticed 

 on the anterior and posterior side of the shell, but in the middle they become quite 

 obsolete on the ribs, and can hai'dly be traced in the fuiTows between them. The 

 form of the shell is very variable. Young specimens are moderately inflated, 

 sub-quadrangular, anteriorly rather strongly compressed, and the lunula is com- 

 paratively narrow. In advanced age the shell rarely increases proportionately in 



