354 CRETACEOUS PELECTPOBA 



4. Trigonoaeca Gamana, Forbes, PL XX^ Eigs. 4-5, and PL L, Eig. 7» 



1846. Area Gamana, Forb., Trans. Geol. Soc, Lond., vii, p. 148, pi. xvi, fig. 3 — eadem auctorum. 



1847. Ar, similis, d'Orb., Yoy. Astrolabe, pi. iv, figs. 33-34. 



Trig, testa oblique trapezoidea, inflata, crassa, sub-incequivalvi, antice sensim 

 angmte sub-rotundata, postice valde carinata et producta, declivitate postica abrupta^ 

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

 sulcis profundioribus intersectis, parte postica scepe costulis radiantibus nonnullis sub- 

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

 longloribus, obliquis, 5-6 in utroque latere, in margins cardinali recto 20-26, ad 

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

 elevata sit a. 



Height of shell : its length ... ... ... 076 - 0-80 



Thickness „ : „ ... ... ... 070 - 072 



This species appears closely allied to Trig, Trichinopolitensis, differing from 

 it by a more solid structure of the shell, which also is more inflated ; it possesses a 

 wider ligamental area, and has the anterior part conspicuously narrowed; the 

 radiating striae are either very faint or more often quite obsolete. Of European 

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

 higher. 



Localities, — Poodoor, Odium, Monglepaudy, &c., mostly in a brownish calca- 

 reous sandstone ; not uncommon. 



Formation, — Ootatoor group. 



5. TiiiGONOARCA BuAHMiNiCA, Forbcs, PL XVIII, Eig. 13, and PL XX, 



' Figs. 1 and 3. 



1846. Area hrahminica, Forbes, Trans. Geol. Soc, Lond., vii, p. 149, pi. xvi, fig. 1 — eadem auctorum. 



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



Trig, testa sub-quadrangulari, inflata, antice leviter rotundata, postice plus 

 minusve producta atque oblique truncata, area in speciminibtts junioribus sub-angusta, 

 in adultis latissima ; superficie striis concentricis crassiusculis, filiformibus, confer- 

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



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



Thickness „ : „ ,.. ... ... 0*68 - 0'90 



The 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 oi! the ribs, and can hardly be traced in the furrows 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 



