166 PAPEUS, ETC. 



from specimens for which I am indebted to M. Eugene 

 Deslongchamps, of Caen. They were found in the Upper 

 Lias of May, associated with several of the species found 

 in this country. It appears to be abundant in France, and 

 to attain larger dimensions than any other liassic Leptasna. 

 I have found a single dorsal valve of this species in the 

 Upper Lias of Ihninster, which though not in good con- 

 dltion, sufficiently identifies the LeptcBna Davidsonn as a 

 British species. 



THECIDEUM, Defrance. 

 Thecideum ornatüm, Moore. 

 Ph II., figs. 1-3. 

 Shell inequivalve ; punctuate, rather rugose, front deep, 

 rounded ; attached by a considerable portion of the ventral 

 valve ; beak slightly incurved ; deltidium small and de- 

 pressed. The ventral valve is flattened on its under side. 

 Its interior is surrounded by an elevated, slightly granu- 

 lated margin. Under the deltidlmn are seen two raised 

 oval processes, separated by a longitudlnal septum, which 

 occupies the greater length of the shell. The exterior of 

 the dorsal valve is rugose and flattened. The interior 

 possesses a narrow, thin, punctuated margin, immediately 

 succeeding which is a ridge of single granulations, which 

 are stronger towards the frontal margin, gradually disap- 

 pearing as the ridge passes upwards. Springing from the 

 centre of this granulated ridge is a septum, slightly taper- 

 ing from its base, on either side strongly serrated, between 

 which is a central longitudinal groove. The septum occu- 

 pies nearly the whole height allowed by the cavity of the 

 shell, and divides it to nearly three-fourths of its length. 

 From the top of the septum there are thrown ofF two 

 extremely delicate lamellae, forraing a loop which curves 



