Silurian Fossils. 



315 



These remains are quite common in the Silurian rocks of Canada, 

 and wherever a river has worn away the loose soil, and in low 

 water leaves a few yards of flat rock bare, the remains of Orthocer- 

 atites may be seen. In some of the species the siphuncle wa& 

 composed of a number of more or less globular divisions, and in 

 such instances, where it is seen imbedded in the stone, it bears a 

 certain resemblance to the back-bone of a fish. The rings of the 

 siphuncle represent the joints, and the septa the ribs, and they 

 are often mistaken for the remains of vertebrated fishes, although 

 none of that department of animated beings existed in the Silurian 

 seas. Many of the species were of diminutive size, in fact mer© 

 pigmies when compared with some of their gigantic brethren,. 

 Two of these we shall figure in the present article, leaving the 

 discussion of the others for the next number of this periodical. 



Fig. 3. 



FijT. 2. 

 Fig. 2. Oncoceras constrictmn. — Hall. ' 



Fig. 3. A section across Oncoceras constrictum, at the up^er 

 chamber from a to b' 



The word Orthoceratite is derived from two Greek words : 

 orthos, straight, and keras, a horn, meaning literally a straight 

 horn. The Orthoceratites are all straight. The word Oncoceras 

 is from the Greek onkos, a bending or protuberance, and keras, a 

 horn. The fossil of which the word is the generic name is not 

 qmte straight but curved, as above represented in Fig. 2. The 

 largest are scarcely four inches in length. They are usually found 

 m the condition of casts or moulds of the interior, the tubular shell 

 having been destroyed. These casts shew all the septa, and the: 

 form of the large chamber in which the body of the animal was 

 contained. This species is slightly curved,^ ventricose in iho. 



