MEDINA SANDSTONE. 



13 



395. 15. MURCHISONIA? CONOIDEA (n. 5j9.). 



Pl. IV. Fig. 7. 



Shell extremely conical ; volutions about four or five, flattened, showing (in the cast) a slight 

 elevation a little below the middle ; character of the surface unknown. 



The individual figured is the only one of the species known. It differs from the species of 

 this genus in the lower rocks, and, in its flattened volutions, approaches some of the forms in a 

 higher position. 



Position and locality. This species occurs in the upper gray portions of the sandstone at 

 Lockport. {Collection o/Col. Jewett.) 



396. 7. BUCANIA TRILOBATUS. 



Pl. IV (bis). Fig. 5 a, b, and part of 3 d. 



Planorhis trilobatus. Conrad, Annual Report 1838. p. 113; 1839, p. 65. 



JBellerophon trilobatus. Hall, Report of the 4th Geol. District, 1843, pag. 48, figs. 6 & 7. 



Not £. trilobatus, Mukchison, Silurian System pag. 604, pl. 3, fig. 16. 



Shell suborbicular, convoluted, three-lobed ; volutions all visible, the last one greatly 

 expanded ; aperture much wider than long. 



This shell bears a close resemblance to Bellerophon trilobatus of Murchison ; but the dif- 

 ference of geological position is very great, and our shell is usually less expanded at the aperture 

 than the figure of Murchison. The middle lobe is broader than the lateral ones, but the apparent 

 proportions are often changed by distortion of the shell from pressure. No perfect specimens 

 have been seen. 



Fig. 5 a. Side view of a specimen. Fig. 5 b. Dorsal view of the same. 



Fig. 3 d. The upper figure in this specimen, and the lower lefthand figure, are of this species. 



Position and locality. It is associated with Pleurotomaria pervetusta in the sandstone at 

 Medina. It occurs likewise in the Clinton group (See Plate 28, fig. 9). {State Collection.) 



397. 2. ONCOCERAS GIBBOSUM (n. sp.). 



Pl. IV (bis). Fig. 6 a, b, c. 



Fragment subcylindrical or fusiform, slightly curved ; section broadly elliptical, the largest 

 diameter of the specimen being at the commencement of the septa ; outer chamber gradually 

 diminishing towards the aperture, slightly curving, and gradually contracting from the same 

 point towards the apex ; siphuncle dorsal ; septa distant about one-eighth the diameter. 



This specimen has all the general characters of the Oncoceras of the Trenton limestone, 

 though it is an entirely distinct species. It diminishes much less abruptly in either direction 

 from the last or outer septum, and is otherwise dissimilar. The outer chamber appears to be 

 nearly entire, and has a depth of scarcely three-fourths of an inch. From pressure, the siphuncle 

 appears less perfectly dorsal in the figure than is really true, but this is due to accident. 



