Some neiv Upper Greensand Bivalves. 123 



apparently of a new genus ; but the lower valves have not yet 

 been seen. There are two species. 



The following characters are probably generic : — " Shell thin, 

 attached, smooth or reproducing the sculpture to which it is 

 fixed. Hinge-line straight. Posterior end gaping. The hinge 

 has a ledge for lodging a tooth, ossicle, or internal cartilage. 

 The anterior muscular impression is near the hinge; from it 

 descends the pallial line in a curve to near the base ; it is then 

 bent back so as to form half a cresceut, and continued along 

 the shell at about one-third its width from the hinge.^^ 



These structures would appear to give it a place between the 

 Tellinidse and Solenidse ; but, as the internal characters were not 

 quite clear, the shells are provisionally referred to Anomia, which 

 externally they much resemble. 



t Anomia transversa. PI. VI. fig. 8. 



Shell ovate, elongated, inflated. Umbo large, prominent, and 

 inclining to the posterior end rather than central. 



This species appears to have been attached to Pectens, and in 

 such a way that all the specimens I. have seen (five) repi'oduce 

 the plications at right angles to their long diameter. As, the 

 shells increased in size, the lower valve probably became free at 

 its margin, for the margin of the upper one is smooth. Attached 

 by the left valve. 



Rare. Coll. University ; J. Carter, Esq. 



The other species is smooth and more elongated. 



Trigonia Hunstantonensis *. PI. VI. fig. 9. 



Form an ovate rectangle, narrow at the posterior end; com- 

 pressed. Ornamented by rowsf of large tubercles, which 

 are oblique and not strictly parallel. They also form rows at 

 right angles with these. Between those in the antero-posterior 

 direction the spaces are much wider than between the rows 

 from hinge to base. The tubercles do not appear to have 

 extended beyond the pallial line. There are faint traces of a 

 posterior area^ the line marking which descended from the pos- 

 terior side of the umbo, curved below the muscular impres- 

 sion, and continued horizontally to the edge (fig. 9 a). It 

 was probably marked with a few narrow ridges parallel to the 

 hinge-line. 

 The cast would indicate a thin shell marked with close regular 



* Hunstanton is pronouuced by the natives Hunston; the specific name 

 mio;ht be similarly shortened. 



t In the cast there arc five or six rows ; but the shell probably had more 

 than twelve. 



9* 



