Logan.] The Invertebrates, Benton Group. 465 



ventral to the peripheral side, and showing all the inner turns ; 

 volutions increasing greatly in size, very slightly embracing, so 

 as to be nearly flat on the sides, but rounding into the umbilicus ; 

 periphery rather narrow, nearly flat, and provided with a small 

 mesial carina, which is very slightly waved in outline ; lateral 

 margins of the periphery each having a row of small, com- 

 pressed nodes, arranged at the termination of each of the costee, 

 with their long diameters nearly parallel to the peripheral keel ; 

 sides of each turn ornamented by from thirty-six to forty rather 

 obscure, slightly flexuous costse, only every second, third or 

 fourth one of which extends across the umbilical margin, where 

 they are usually a little swollen. The septa are generally a 

 little crowded in adult shells, and divided into two very 

 unequal principal lobes on each side. Siphonal* lobe rather 

 longer than wide, ornamented by three branches on each side, 

 the two terminal of which are a little larger and much less 

 spreading than the lateral pair, and each ornamented by some 

 five or six sharp digitations along the margin and at the 

 extremity, where the first pair of principal lateral branches 

 above the terminal ones are of nearly the same form as the 

 latter, but more spreading, and the third pair are smaller, and 

 merely provided with a few digitations ; first lateral sinus 

 (dorsal saddle of old nomenclature) as long as the siphonal 

 lobe, but much wider, and deeply divided into two unequal 

 parts, of which the one on the siphonal side is larger than the 

 other, each of these principal divisions being ornamented by 

 some four or five short, irregular branchlets, with obtusely digi- 

 tate margins ; first lateral lobe slightly wider than the siphonal, 

 and provided with some seven or eight short, rather unequal, 

 merely digitate, and palmately spreading terminal and lateral 

 branchlets ; second lateral sinus narrower, but as long as the 

 first on the outer or siphonal side, and much shorter on the 

 umbilical, having two short, unequal, digitate branches at the 

 end, and some three or four short, irregular divisions along the 

 oblique margins of the umbilical side ; second lateral lobe small , 

 or scarcely more than twice as large as the auxiliary lobe of the 

 siphonal sinus, and somewhat irregularly bifid, the divisions 



