No. 2.] 



BILLINGS — PALEOZOIC FOSSILS- 



213 



ON SOME NEW SPECIES OF PAL^OZOLC FOSSILS. 



By E. Billings, F.G.S. 



© 



Fig. 1. Ilyolithes communis. 2. H. Americanus. 3. H. ? micans. 

 4. H. princeps. In these diagrams a i\'presents the rate of tapering 

 of the shell on the ventral side ; b, the transverse section (except in 

 3 6, which is the inner surface of an operculum enlarged two diame- 

 ters). The small figure in 3 a represents tlie apical portion of a 

 specimsn. N.B. — All these species vary slightly in the rate of taper- 

 ing. 



Genus Hyolithes, Eichwald. 



In the following description of new species of Ili/olithes, I shall 

 call the side of the fossil which is most flittened, or from which 

 there is a projection in front of the aperture, '- the ventral side." 

 Directly opposite is the " dorsum." The lateral walls, whether 

 consisting of two sloping planes, as in fig. 2, or rounded as in the 

 other figures, I shall designate simply •' the sides." The '• width " 

 of the aperture is the greatest distance between the two most 

 projecting points of the sides. This is sometimes close to the 

 ventral side as in tig. 2. The '- depth " is the distance between 

 the median line of the ventral side and the dorsum, and is at 

 right angles to the width. That part of the ventral side which 

 projects beyond the aperture is the " lower lip." The " ventral 

 limb " of the operculum is that side which is in contact with the 

 lower lip, when the operculum is in place, in the aperture. The 



