NO 3.] DESCRIPTION OF THE FOSSILS. 59 



growth at the posterior margin (PL I. figs. 7, 8) completes its similarity to 

 the English specimens. 



The places of the attachment of the muscles, which permitted of being 

 prepared in one of the specimens (PI. I. fig. 6) correspond as nearly as possible 

 with those of specimens from Yorkshire. In fig. 6 (6a) a rather long reniform 

 impression may be seen on the cast on both sides beneath the apex. The 

 impressions become slighter towards the fi'ontal side of the valve, so that 

 their anterior extremity is not very distinctly marked. The impressions on 

 the casts correspond with thickenings on the inside of the valves which 

 in Discina serve as attachments for the muscles. Upon the plain, extending 

 from the apex to the frontal margin, two broad, quite smooth radial, elevations 

 may be observed. 



On the casts, both here and in specimens from Yorkshire, may be 

 observed extremely fine ribs radiating from the apex to the frontal margin. 



The form represented in fig. 9 is particularly flat, and hence recalls 

 Discina Etheridgei Dav.^ from the Inferior- Oolite-Sands of Nailsworth. It 

 differs from that species in the distinctly marked apex (broken off in this 

 specimen). Judging from the form of the attachments of the muscles, Discina 

 Etheridgei Dav. is only a flatter variety of Discina reflexa Sow. sp. with- 

 out distinctly marked apex. 



The fragment (cast) represented in fig, 10 differs somewhat in the 

 position and form of the apex from the other pieces, and also from other 

 specimens of Discina reflexa Sow. sp. which have been examined. The apex 

 is perfectly central, curving somewhat towards the posterior margin (the piece 

 is reversed in the drawing). Owing to the imperfect condition of this piece it 

 is impossible to determine with certainty whether it should be identified with 

 Discina reflexa Sow. sp. or not. 



MOLLUSC A. 

 LAMELLIBBANCHIA TA, 



It is only in the hard, grey, sandy marl (No. 4), that lamellibranchs 

 occur in any great quantities. Unfortunately, however, none of the numerous 

 forms contained in this rock, with the exception of the new Pseudomonotis 



1 Th. Davidson, 1876, 1. c. p. 86, pi. X, fig. 20. 



