HETEROPODA AND PULMONIFERA. 



41 



lip and a notch in the upper lip — characters which are not 

 present in Machirea. It is a matter of question whether 

 OijliiUta should be regarded as comprising species of Mac- 

 lurm with slender whorls, or whether it should be placed 

 in the Littorinidce, in or near Euomphcdus, as has been pre- 

 viously mentioned, or whether it should not be placed in 

 the Haliotidcc and be regarded as a discoidal Pl&urotomaria. 



Pig 430 — OphiUta hella (Billings). Different views of a nearly peifect specimen. 

 Quebec Group (Lower Siluiian). 



In the genus Cyrtolites (fig. 431) the shell is thin, sym- 

 metrical, discoidal, or coiled into the shape of a horn, the 

 whorls more or less disconnected, furnished 

 with a keel, and sculptured. The species of 

 this genus range from the Lower Silurian to 

 the Carboniferous rocks, and are therefore 

 exclusively Palseozoic. 



In IJcculiom'p'halus (fig. 432) the shell is 

 very like that of Cyrtolites, but the whorls 

 are few in number, and are widely separated 

 from one another. The shell is thin, and the 

 coils lie in the same plane. The species of 

 this genus range from the Lower Silurian to 

 the Carboniferous, and have been compared to Euomi^Mli 

 imperfectly rolled up ; but the true affinities of the genus 

 are doubtful. 



Section B. Pulmonifera. — Eespiration aerial, by means 

 of a pulmonary chamber. The Pulmonifera include the 

 ordinary Land-snails, Slugs, Pond-snails, &c., and are usually 

 provided with a well-developed shell ; though this may be 

 rudimentary (as in the Slugs), or even wanting. In the 



Fig. AZl.— Cyrtolites 

 ornatus. Lower Silu- 



