OP SOUTHEUN INDIA. 89 



PANOP^A, Menard, 1807 (seep. 85). 

 \y^ 1. Panopj]]A omentalis, Forbes, PL II, Figs. 1-4. 



1846. 'Panojpcea orientalis, Forbes, Trans., Geol. Soc, Lond., vii, p. 139, &G.~idem auctorum ; (nomeii 

 P. orientalis, Con., (Off. Eep. in Lyncli's Exped., Palest., dubiosum). 



P. testa ovato-elGngata, valde incBquilaterali, parte antica multo breviori, sulco 

 lato sed hand prof undo ab aplcibus ad marginem inferior em subrecte decurrente 

 separata, lateribus anterioribus rapide declivis, infra Mantibus ; parte postica 

 gradatim plus minusve attennata^ ad terminationem rotundata ac late hiante ; 

 superficie striis minutissimis ac sulcis costulisque angnstis, imprimis prope apices 

 distinctis notata. 



Greatest height of shell : its length ... ... .,, 0-64 



Thickness „ : „ ... ... ... 048 



The form of the shell of this species is very characteristic, but as reo'ards 

 the posterior attenuation somewhat variable; the anterior part of the shell is 

 truncated in front and separated from the posterior by a broad, though shallow, 

 furrow extending from the beaks to the antero-inferior margin. The middle portion 

 of the lower edge is convex ; the concentric sulcations are as usually most distinct 

 near the beaks ; the fulcra are long, thickened, but not very prominent. The right 

 valve has an erect tooth in front of a pit to which the tooth of the left valve 

 corresponds. 



Localities, — Anapaudy, Koloture, Serdamungalum, North of Alundanapooram, 

 &c., and south of Arrialoor ; mostly in bluish, brownish, and whitish sandstones. 



Formations. — Trichinopoly and Arrialoor groups ; very common in the former, 

 rare in the latter. 



VII. Family, —GLA UCONOMYIDJE. 

 The animals of the species belonging to this family are, in external appearance, 

 very similar to those of the myin^ on the one side and the anatininje on the 

 other ; they have the mantle margins united, open anteriorly for the protrusion of 

 only a small, more or less elongated foot ; the gills are double, rounded, about 

 half the length of the body, and one-third longer than the palpi, which are broadly 

 falciform. The gills are not prolonged into the siphons* which are united up to 

 the end, with the orifice free and fringed ; they are enveloped in an extension of a 

 more or less thickened or coriaceous epidermis which covers the shell, similarly as 

 in Mya or Anatina, At the base of the siphons there is a very small opening in 

 the mantle through which a portion of the water which enters the body is at 

 intervals ejected with force, while the current in the in-and ex-haling siphons is a 

 more regular and continuous one. A similar opening below the siphons is also 

 found in NovacuUna (and several other Solenid^), serving the same purpose. 



* In Glauconomya cerea, which is found along our sea coast, Mr. W. T. Blanford tells me the siphons are rather 

 thin and of nearly double the length of the body. This coincides with an observation I lately made on a species 

 occurring on the sandy beach at Arracan. 



