OP SOUTHERN INDIA. 449 



minore magisque obliqtm, utraque ah corpore testce jugo foliose costulato separata ; 

 area angusta, latissime trigonata, paulo declivi ; cardine dentibus externis crassis 

 et fovea ligamentali mediana, suh-quadrata, imtructo. 



D'Orbigny long since suggested that the two forms, described by Porbes 

 under diflferent names, belong to the same species. There can be little doubt on this 

 point, however different the shells appear at first sight. In some specimens the 

 upper valve has very few stronger ribs, in others they are numerous, there being two 

 to five thinner ribs between each two thicker ones. The former are slightly undu- 

 lating and finely rugose on account of the striae of growth crossing them, the 

 latter are at shorter or greater distances enlarged into broad, scale-like tubercles. 

 In young specimens there are always only very few stronger ribs present. The 

 ears of the upper valve are unequal, the posterior being smaller and more oblique 

 than the anterior ; each of them is separated at its base from the shell by a rugose, 

 foliaceous ridge, of which the anterior is sometimes represented by an oblique 

 series of transverse, elongated tubercles. This character indicates a strong relation 

 of the Indian form to the European Sp, truncatus, Goldf., but in this species the 

 stronger ribs never attain the same thickness, and the tubercles on them are much 

 more compressed, cristate. 



The lower valve varies in size : the umbonal part being more or less produced 

 and with a larger or smaller area attached. In some specimens it is conical, with 

 the umbonal part distinctly twisted. The radiating ribs on it are not much raised 

 above the surface and equal, but the concentric lamellae are strongly prominent, 

 sharp, lamellar, some of them continuous, others partially interrupted. The 

 internal edges of both valves are, as usually, toothed all round the margin. 



Localities, — Near Coonum and near Serdamungalum, in^grey sandstone. 



Formation, — Trichinopoly group. 



4. Spondylus sub-costulatus, StoliczJca, PI. XXXIII, Pig. 8; PL XXXIV, 



Pig. 2. 



Sp, valva inferior e tumida, convexa, ad umhonem plus minusve tate affixa, 

 radiatvm costellata et concentrice striata, ^triis sulcis nonnullis profundioribus inter- 

 sectis, hand lamellosis ; valva supera elongate, vel late, ovata, convexa, ad umbonem 

 scEpe gibbosa, radiatim costulata, costulis cequalibus, hand tuber ctilatis. interstitiis 

 aut cequidistantibus aut angustioribus ; auriculis incequalibus, Icecigatis, auricula 

 postica minore, angusta, margine superiore valde obliqua. 



The form of the shell is somewhat variable in this species ; it is either elon- 

 gately or roundly ovate, sometimes irregular, evidently depending upon the surface 

 of the object on which the lower valve was sessile. The numerous, rather fine, 

 and equal ribs, without any larger tubercles, and the smooth unequal ears of the 

 upper valve, readily distinguish the species from others. The furrows separating 

 the ribs are either narrower than the ribs, or they equal them in width ; but these 



5 s 



