HILDOCERAS. Ill 



gation I was not satisfied, and so I removed the test as much as possible from the 

 sutures of the actual Lillia sulcata, and the result is given in Plate XXIII, fig. 1. 

 In order to show the specimen from which the former suture-line (Plate XXII, 

 fig. 34) had been taken — and which specimen will be described at a later portion 

 of this work with the other members of its genus, Sonninia — I had two views 

 of it inserted where it could be compared with the other specimens, and especially 

 with Lillia sulcata. 



Plate XXII, figs. 32, 33, give the side and front views of this species. The 

 specimen came from Bradford Abbas, and from its matrix I judge it to be from 

 Bed 3 of the section at page 5 (Humphriesianum-zone) . It is in my collection. 

 Plate XXIII, fig. 1 , exhibits a portion of the suture-line taken from the same 

 specimen. 



HildoceratiDjE (continued). 



Genus — Hildoceras, 1 Hyatt. 



1867. Hildocebas, Hyatt. Fossil Cephalopoda, Museum Comp. Zool. Bull., 



vol. i, No. 5, p. 99. 



(Type — Hildocebas bifbons, Bruguiere sp.) 



Definition. — Discoidal, compressed, carinate, widely umbilicate ; whorls sub- 

 quadrate, ornamented in the type-form with well-marked sigmoidal ribs, which have 

 the genicula close to the inner margin and the outer arc very long. 2 (In some 

 species the ribs are straight on the lateral area.) Ventral area with deep furrows 

 each side of the carina when the test is absent, but sometimes the furrows are 

 inconspicuous when the test is present, more especially in adults. Carina solid. 

 Inner margin subconcave, sloping. Suture-line : 3 Siphonal lobe with two 

 terminal points closely embracing the siphuncle ; siphonal saddle very broad, and 

 with a very small accessory lobe ; superior lateral lobe broad, inclined to be 

 bulbous and very little branched, with no actual trifurcation ; inferior lateral lobe 

 about one-fourth the size of the superior lateral, inferior lateral saddle, auxiliary 

 lobes and saddles sometimes elevated, sometimes hanging down, and varying 

 in this and other respects according to the amount of involution. The general 

 tendency of the genus is to be latisept, but specimens of the same species and even 

 parts of the same individuals vary in this respect. 4 



1 St. Hilda. 2 Plate A, fig. 30. 3 Plate A, figs. 28, 29. 



4 One specimen of Hildoceras bifrons (compressed variety) shows half the whorl latisept, the 

 other half densisept. Other specimens show considerable irregularity in this matter. 



