NOTES ON A COLLECTION OF SILURIAN FOSSILS — AMI. 413 



growth which are crossed by much finer and much more 

 numerous radiating lines which are on]y visible with the aid of 

 a lens. 



Lower or attached valve, unknown. Dimensions of the cast 

 of the interior of a fine specimen, as follows: Length, l7f milli- 

 metres ; breadt/i, ISi millimetres ; height of the free valve, 

 nearly 2 millimetres. 



6. DisciNA ORiENTALis, N. SP. Besides the two foregoing 

 species of this genus examined from the limestones of Cape 

 George, there occurs also a comparatively small ovate-elliptical 

 form in the collection. 



The shell is moderately elevated, and the executric apex is 

 situated at about one-fourth the length from the posterior 

 margin, and forms a curve round from that margin to the side. 

 Surface is marked by obscure concentric lines of growth, and 

 faint radiating lines from the apex. 



This form difiers from either of the two just described, 

 in being more narrowly elliptical, in the position of the apex, 

 and in its peculiar twisted or curved character, as above 

 indicated. 



In some respects it approaches Discina Morrisii, Davidson, 

 from the Wenlock limestone of England. 



7. LiNGULA RECTILATERA, Hall. — There are several specimens 

 and fragments of a Lingula in the collection, amongst which 

 some are tolerably well preserved. They agree in every respect 

 with Prof. Hall's species (L. rectilatera) described in his " Palaeon- 

 tology of New York, vol. 3, p. 156, figured on plate 9 — figs. 6 

 and 8. 



8. LixouLA sp. — This form resembles Lingitla perovata, Hall 

 — described from the upper green (Clinton) shales of Rochester, 

 N. Y. Only one specimen of this species occurs in the collection. 

 It agrees fairly well with Hall's descriptions given of Lingula 

 jperovaia. 



9. Orthis assimils ? Hall. — There is the cast of a species of 

 Orthis in the collection, which cannot be satisfactorily distin- 

 guished from the above as described by Prof. Hall, and has there- 

 fore been referred to it, but with some degree of uncertainty. 



