PERNA. 95 



Measurements : 















(i) 



(2) 



(3) 



Length 





58 



46 



32 mm. 



Height 





87 



70 



47 „ 





(1 



— 3) Cambridge 



Greensand. 





Type. — From the Cambridge Greensand. In the Sedgwick Museum, Cambridge. 

 Distribution — Cambridge Greensand (derived, internal casts). 



Perna, sp. Text-figures 19, b o. 



1861. Perna lanceolata, H. G. Seeley. Ann. Mag. Nat. Hist., ser. 3, vol. vii, 



p. 122. 



Remarks. — This species (figs. 19 b, o) was referred by Professor Seeley to 

 Perna lanceolata, Geinitz, 1 and it presents a general resemblance to the examples 

 figured by Reuss and by d'Orbigny, but is less oblique. No satisfactory com- 

 parison, however, can be made, since the specimens from the Cambridge 

 Greensand are in the form of internal casts. 



Some examples (fig. 19 e) were named Perna lanceolata, var., by Seeley; the\ 

 differ from Geinitz's species in the postero-ventral part being more produced and 

 less rounded, so that the outline of the valve becomes more distinctly quadrate. By 

 this quadrilateral outline they are distinguished from P. Bauliniana. 



Distribution. — Cambridge Greensand (derived, internal casts). 



Perna, sp. Text-figure 19 p. 



1861. Perna subspathulata, H. G. Seeley. Ann. Mag. Nat. Hist., ser. 3, vol. 



vii, p. 124. 



Remarks. — Internal casts were regarded by Professor Seeley as examples of 

 P. subspathulata, Reuss, 2 but they appear to differ from the latter in their 

 greater convexity. The height is less and the length greater than in P. obloiiga. 



Distribution. — Cambridge Greensand (derived). 3 



1 'Das Elbthalgeb. in Sachsen,' pt. i (1873), p. 210, pi. xlvi, fig. 8. References to other figures 

 are given by Geinitz. 



2 ' Die Verstein. der bolim. Kreideformat.,' pt. ii (1846), p. 24, pi. xxxii, figs. 16, 17. 



3 Avicula cuneata, Seeley, may be a Perna. Perna lissa, P. plana, and P. transversa, Seeley, 

 appear to be Inocerami. All four come from the Red Limestone of Hunstanton. Seeley, ' Ann. Mag. 

 Nat. Hist.,' ser. 3, vol. xiv (1864), p. 277, and vol. xvii (1866), pp. 178, 179. 



