242 CEETACEOUS PELECYPODA 



anastomosing, but very thin canals ; at the aperture these lamellae form a large 

 margin, being only interrupted by a broad bipartite, smooth area which runs from 

 the apex to the margin. What the nature of this flattened or partially excavated 

 area is, it is difficult to explain. It certainly must be caused by a peculiarity 

 of the mantle margin, but it does not correspond to the hinge area of Ostrea 

 or Spondylus, The hinge lies (see h in figs. 2 and 3 on pi. xxi) somewhat 

 below to the left of this area, where the two bifid ribs are internally situated, in 

 which the edges of the concave cartilage-plate of the upper valve fit. Next to 

 the cartilage-plate in the free valve are the elevated, roughly striated muscular 

 ridges. In figs. 3 and ^a on plate xxii the different parts are also noted in detail. 

 The only probably correct suggestion regarding the presence of that bipartite ex- 

 cavated area is, that it may have been produced by the produced siphonal openings 

 of the animal, for it is situated behind the posterior muscular impression. 



Locality. — Comarapolliam, in a light grey conglomeratic sandstone ; very 

 common. 



Formation. — Arrialoor group. 



SPHiERULITES, de la Merth, 1805, (see p. 238). 

 y SPHiERULiTES iNDicA, StoUczka, PL XXI, Eig. 4, PL XXII, Eig. 4. 

 Sph. valva inferiori cylindraceo conica, elongata, moderate curvata, in superficie 

 costis numerosis acutis multilamellosis quarum nonnullis (?) fortiorihus ornata intus 

 costa unica longitudinali instructa apertura suhrotundata^ ad marginem undique 

 expansa et radiatim cos fat a. 



This is a very solid, elongately conic, slightly curved form, gradually increasing 

 in thickness. The surface is ornamented with longitudinal ribs, which are sharp and 

 strongly lamellated. Some of the ribs appear to be stronger at one side, but 

 none of the specimens examined is so far perfect as to show their number and 

 relative size clearly. The aperture is roundish, with the margin largely expanded 

 and radiately costulated. The inner layer of the shell is, as in Badiolites, thin, but 

 shows only a single longitudinal so called hinge-rib. A tolerably perfect specimen, 

 partially a cast, does not show any concameration towards the apex. 



Together with three fragmentary specimens of the lower valve one upper valve 

 was found ; it is figured (fig. 4) on plate xxii. Erom its resemblance to that 

 of other authentic SphcErulites, it is probable that it belongs to the present species, 

 though no decisive proof can be given. The figure shows the internal side, the 

 other side being so thoroughly cemented to the rock that it is impossible to 

 detach it. This internal view shows the valve to be slightly excavated, of a 

 roundish oblong form, with concentric undulating stride of growth, shelving edges 

 all round, and an internal sharp ridge proceeding from the margin towards the 

 centre. The median part itself appears to have been injured, and very likely the 

 cartilage-plate and the muscular ridges were broken off, but they could not have 

 been of any considerable strength. 



Locality .—OAm-m, in a brownish earthy limestone ; apparently very rare. 



Formation. — Ootatoor group. 



