Silurian Fossils of Nova Scotia, 155 



This species is remarkable for its extremely gently tapering 

 form ; the fragment of more than an inch long, showing scarcely 

 a perceptible diminution in diameter. There are twelve and a 

 half chambers 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.* 



Fig. 16. 



29. CoRNULiTES rLEXUosus. 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 comparative dis- 

 tance of the annulations. None of them, however, are so slender 

 as the Nova Scotia specimens. 



30. HoMALONOTus Dawsoni. N. sp. Fig. 17. 



Caudal shield somewhat parabolic, obtuse at the extremity, very 

 convex, width at the anterior side greater than the length of the 



* The Arisaig beds afford at least three other species of Orthoceras. 

 Cne, the largest of the three, has a marginal inflated siphuncle, and the 

 septa about one-eighth of an inch apart, for a specimen two inches in 

 diameter. It tapers very gently, and in all the specimens found is ellipti- 

 cal in its cross section. It occurs in the upper series. A second, found in 

 the lower series, is marked with strong annulations placed closely to- 

 gether. A third, occurring in the upper series, and discovered since 

 the specimens were submitted to Professor Hall, is a very beautiful 

 species, apparently new, but closely resembling O. 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 stria, scarcely visible to the naked eye, and 

 about sixteen in a line. Under the microscope the striae appear as thin 

 sharp parallel curved ridges, the spaces between being finely granulated 

 and wider than the ridges. I would name this species 0. elegantulum. — 

 J. W. D. 



