206 



Lower Silurian Fossils of Canada. 



of this or else closely related species. It occurs in the Trenton Limestone. 

 The specific name is Latin, Pcctinella, a little comb. 



Fig. 5. 



Fig. 6. 



Fig. 7. 



Fig- 8. Fig. 9. Fig. 10. 



Fig. 5. — Orthis pedinella. Figs. 6, 7, 8, 9, and 10. — Orthis Lynx. 



Orthis Lynx, (Eichwald) commonly called Delthyris or Spirifer lynx, 

 is a very common fossil in the Trenton limestone, at the City of Ottawa. 

 Its form is exceedingly variable, but it is, notwithstanding this, easily 

 recognized in all its shapes. The hinge line is straight, and often prolonged 

 so as to form short, acute ears. Its outline is semi-elliptical, or sub-quadrate, 

 and its surface bears a number of very strong radiating ribs. The ventral 

 valve has a deep sinus in which there are three or four ridges, while the 

 dorsal valve shews a corresponding mesial fold with four or five ribs. Figs. 

 9 and 10 are views of the bottom of the fossil, shewing the large sinus 

 in the margin. ITie beaks are about equally incurved, and the area is 

 narrow, a little largest on the ventral valve. This fossil, usually, has both 

 valves very much curved, and, in consequence, it sometimes approaches a 

 globular shape. It has more the appearance of a Spirifier than of an 

 Orthis, (see the figures of Spirifer radiatus, S. Sidcatus, and S. NiagarcnsiSf 

 Plate 2, in the 2nd number of this Journal, Figs, 3, 7, and 8) and it was 

 imtil lately, most commonly known as Spirifer lynx. It is now, however, 

 considered to be an Orthis. No species of Spirifer is described as existing 

 in the Lower Silurian rocks of North America, in any of the books within 

 our reach, and this shell, therefore, when met with in the Trenton limestone, 

 is easily recognised, as it is the only fossil in the formation which presents the 

 ears and other general external characters of that genus. The specific name 

 was probably derived from the resemblance which some of the specimens 

 bear to the head of a Lynx. The fossil is so variable in its form, that th» 

 figure of one specimen will not closely resemble others found in another 

 locality, and therefore we have given a number from all ofwhich the general 

 idea of the species may be formed. 



