176 CEETACEOUS PELECYPODA 



shells. In well preserved specimens the concentric ribs are thinner as compared 

 with the interspaces in which extremely fine concentric lines are traceable. When, 

 however, the ridges of the ribs are a little worn off and thus become broader, 

 the interspaces have apparently the same width as the ribs. 



Locality, — ComarapoUiam, in a light grey sandstone, apparently rare; only 

 three specimens were as yet found ; all are figured. 



Formation, — Arrialoor group. 



\ 11. Cytheeea [Oallista] vagrans, StoUczka, PL VII, Figs. 21-23. 



Cyth. testa late ovata, seu rotundate quadrangulari, moderate convexiuscula, con- 

 centrice liris subtilibus numerosissimis sulcis angmtis parum profimdis separatis 

 notata ; declivitate lunulare fere recta, areale convexiuscula ; lunula magna, ovata 

 linea impressa marginata, medio elevata ; area minima impressa ; margine antico^ 

 ventrale ac postico uniforme-, ultimo quandoquam levissime- arcuato ; sinu pallii 

 angusto, ohtusiusculo, ascendente, Cardo in valva sinistra dentihus trihus cardinali- 

 hus et uno margine lunulari parallelo instructus ; dentihus cardinalihus duobus 

 posticis in valva dextra ceteris multo crassioribus. 



Length of largest specimen ... ... ... ... 14 m. m. 



Height : length ... ... ... ... 0-75 



Thickness ; height ... ... ... ... 0*66 



Shell ovate or sub- quadrangular, small, moderately convex, with very numer- 

 ous, close concentric not much elevated ribs; beaks prominent, pointed, and 

 incurved ; lunular declivity almost straight, with the lunula ovate, proportionately 

 large, margined by a distinct groove and elevated along the central line ; posterior 

 declivity convex, the area very short, narrow and impressed, with the fulcra hardly 

 distinguishable ; anterior and posterior ends rounded, the former slightly produced ; 

 ventral margin more convex in the oval than in the sub- quadrangular forms; 

 pallial sinus short, narrow, obtuse at the end and ascending. In the left valve 

 the cardinal teeth are thin, except the anterior, which is a little thicker than the 

 rest ; the lunular tooth is elongated and parallel to the margin. In the rio»ht 

 valve (a specimen from ComarapoUiam) the two posterior cardinals are remarkably 

 thick, leaving narrow interspaces between them for the thinner teeth of the left 

 valve. 



Localities.— Qom^m^oWmm and north-east of Karapaudy, in whitish conglo- 

 meratic sandstone (one specimen from each) ; Garudamungalum in bluish calcareous 

 sandstone ( two specimens ) ; south of Garudamungalum in brownish sandstone 

 (one specimen). 



Formation,— AvvmlooT and Trichinopoly groups. The ComarapoUiam specimen 

 is somewhat roundly sub-quadrangular, and has the two posterior cardinals, as 

 noticed above, remarkably thick, but there is no other difference in the ornament- 

 ation and structure of the shell. The specimen from Karapaudy is in every respect 

 identical with those from Garudamungalum, and is the largest. 



