606 THE UPPER SILURIAN. 



bers in the space of one inch. The surface markings are peculiar, and 

 among the species of the genus known to us constitute a distinctive 

 character. Large specimens nearly two inches in diameter from East 

 liiver have the characters of this species. Arisaig, coll. J. W. D. 



Orthoceras elegantulum, Dawson (Fig. 213). This is a very- 

 beautiful species, apparently new, but closely resembling 0. perelegans, 

 Salter, of the Lower Ludlow formation. It is cylindrical, but slightly 

 flattened ; septa very convex and one-twentieth of an inch apart in a 

 specimen half an inch in diameter ; siphuncle central. Surface with 

 slight rounded annulations from one-eighth to one-fourth of an inch 

 apart, and covered with delicate transverse strice, scarcely visible to 

 the naked eye, and about sixteen in a line. Under the microscope 

 the stride appear as thin sharp parallel curved ridges, the spaces 

 between being finely granulated and wider than the ridges. Arisaig, 

 coll. J. W. D. 



Orthoceras (?), n. s. East River, coll. J. W. D. 



Orthoceras (?), n. s. Nictaux, coll. J. W. D. 



Cyrtoceras, n. s. East River, coll. J. W. D. 



Orthoceras exornatum^ Dawson. Arisaig, coll. J. W. D. This 

 species, collected by Dr Honeyman at Arisaig, is circular in the cross 

 section, moderately tapering, and straight ; with the siphuncle slightly 

 excentric, and septa half a line to a line apart, in a specimen two to 

 four lines in diameter. The surface is slightly annulated, and orna- 

 mented with about twenty-four flat longitudinal flutings in the manner 

 of a Doric column. The whole surface is also delicately striated 

 transversely. 



Orthoceras nummulare, Sow. Arisaig, Dr Honeyman. 



Orthoceras Ibex, Sow. Arisaig, Dr Honeyman. 



Orthoceras, like 0. biiUatum, Sow. Arisaig, Dr Honeyman. This 

 and the two last are given on the authority of Dr Honeyman and Mr 

 Salter, who also mention species of Litidtes and Phragmoceras. 



Articulata et Incertce sedis. 



CornuUtes jiexuosus, var. gracilis. This fossil resembles the one in 

 the Clinton group of New York, but is somewhat more slender, and 

 the annulations a little more closely arranged. The specimens from 

 the rocks of New York present some variation in form, and the com- 

 parative distance of the annulations. None of them, however, are so 

 slender as the Nova Scotia specimens. Arisaig, East River, coll. 

 J. W. D. 



CornuUtes (?), n. s. East River, coll. J. W. D. 



Humalonotus Dawsoni, Hall (Fig. 214). Caudal shield somewhat 

 parabolic, obtuse at the extremity, very convex, width at the anterior 



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