OF SOUTHERN INDIA. 395 



Convad (Journ. Acad. Nat. Sc, Phil., 2nd ser., iii, p. 330, pi. xxxiv, fig. 5,) 

 described a Pulclnites argentea* from the Mississippi cretaceous beds, which is, I 

 think, the only other sj)ecies i-eferred to Defrance's genus. 



This is about all we know of the problematic genus PiilmnUcs. It will be 

 interesting to see by further research in what relation these shells stand to the next 

 genus. 



22. Pernostrea, Mun.-Chalmas, 1864, (Journ. de Couch., iii"'" ser., torn, iv, 

 pp. 71, et seq., pp. 362 et seq.). Rounded or oval, solid, more or less tumid, inequi- 

 valve, the left valve being in adult specimens attached ; structure lamellar, resem- 

 bling that of Penia ; beaks usually indistinct, hinge area broad, or with age 

 becoming more or less reduced in extent, with numerous (4 — 8) transverse 

 ligamental grooves or pits, as in Mellna ( = PeriiaJ ; muscular impression rather 

 small, sub-centric, ovately rounded, smaller in the right valve; type, P. Bachelieri, 

 d'Orb. The genus forms a connecting link between Melina (= PernaJ and Ostrea, 

 differing from the former especially by its sessile habitat, absence of a byssal 

 sinus and strongly excavated muscular scar ; from the latter by the presence of 

 separate ligamental grooves. Externally Pet'iwstrea is barely distinguishable from 

 Ostrea. Munier-Chalmas enumerates six species, all from Jurassic deposits. 

 Crosse gave a revision of the genus and established the priority of two species 

 first described by d'Orbigny in his Prodrome, P. Bachelieri and Jjuciensis. 



23. Leproconcha, Giebel, 1856, (Abhandlung. des Nat. h. Ver. f. Sachsen 

 and Thliringen, i, p. 67). A small roundish shell with the lamellar structure of 

 an Ostrea, umboues nearly central, as in Brachiopoda, outer surface tubercular, 

 hinge area with 3-4 ligamental (?) grooves. 



The above name has been proposed for a small triassic shell which Giebel 

 says comes near to PUcatula or Pnlvinites. If the hinge grooves are ligamental, 

 as they are supposed to be, the classification of the genus would be near Puhnnites, 

 but better materials must be examined in order to define the characters of both 

 these problematic genera. 



24. Crenatula, Lam., 1802. Equivalve, or very nearly so, generally thin, 

 obliquely elongated, sub-oval, smooth or concentrically finely lamellated ; beaks 

 obtuse, almost quite anterior, posterior hinge line straight or slightly undulating, 

 with numerous ligamental pits ; muscular scars oblong, indistinct ; type, C. aci- 

 cularis, Lam. Reeve (Iconica, vol. xi,) describes eight species, all, with one 

 exception, from the Red Sea. The species live in sponges, which accounts for their 

 thin structiu-e. No fossil species of the genus are known, unless some of the 

 ii"regularly shaped Melince belong to it. 



25. Ilellna, Retzius, 1788, f Isognomo)i,\ Klein, 1753, ex 2J('>'te ; Perna, 

 Brug., 1792, non Adanson). Equivalve, or sub-cquivalve, irregularly rounded or 



* See also Am. Journ. Concliology, III, p. 9. 



t I do not think that Klein's name Isocjnomon can safely he accepted. His figure (Ostrac, pi. viii, fig. 15,) may 

 as well represent a variety of some Malleus, but on the same plate he figures (fig. 18) a true McHna under the name 

 of Mater perlarum, and figs. 19 and 20 would appear to represent a Crenatula, and are called Ostrteum IcBve. 



5 D 



