GYROCERAS. 91 



1. Gyroceras PRyEOLARUM, WJiidborne, sp. PL VIII, figs. 1 — 3. 



1841. Ctetoceeas OENATtJii, Fhil. (not Ooldfuss). Pal. Foss., p. 115, pi. xlv, 



fig. 217. 



1888. — — Etheridge. Foss. Brit., vol. i, Pal., p. 167. 



1889. — PE^CLAEUM, Whidbortie. Geol. Mag., dec. 3, vol. vi, p. 29. 



Description. — Shell large, highly ornamented, tapering slowly, loosely coiled in 

 an open elliptic spire of at least 1^ volutions, of which only about one-third 

 of the ventral side of the volution near the apex is in contact with the dorsal 

 side of the external whorl. Spire somewhat unsymmetrical, but sunk much below 

 the summit of the outer whorl. Section irregularly elliptic, being obliquely 

 flattened on the ventral and dorsal aspects. Ratio of the ventro-dorsal to the 

 lateral diameter as 2 : 3 or as 3:4; these axes being set rather obliquely to the 

 plane of the whorls, and. changing their direction from side to side with the 

 growth of the shell. Apex spheroidal, rather swollen dorsally. Chambers 

 shallow, concave. Siphuncle situated close to the ventral margin. Surface 

 ornamented with thirty or forty low, rounded, small, and distant longitudinal ribs, 

 sometimes with a smaller alternating series between them, which are crossed 

 obliquely by very numerous close fine threads, and by a few rather distant pro- 

 minent ridges or bulges, which rise on the lateral parts of the dorsal surface, cross 

 the whorls rather obliquely, and are deeply but irregularly arched back over the 

 syphonal area ; these ridges forming in the apical portions (or in the younger shell) 

 almost smooth folds, posteriorly sloping, anteriorly steep ; but, as the shell grows, 

 becoming more and more nodulous on the ribs, till in the aged shell they are occa- 

 sionally developed into coarsely membranaceous horns or peaks on the sides of the 

 whorls, which are represented in the cast by large transverse nodes. 



Size.- — The portion of the aged shell figured by Phillips measures 93 mm. in 

 length, 35 mm. in ventro-dorsal, and 50 mm. in transverse diameter at the larger 

 end. The young but nearly perfect specimen in the Museum of Practical Geology 

 measures 50 mm. in length, 30 mm. in width of the spire, and about 25 mm. in 

 depth; and Mr. Vicary's aged, almost perfect shell measures 77 mm. in length, 

 82 mm. in width of spire, and 48 mm. in depth. 



Locality. — Wolborough. Phillips's original specimen, and a similar but 

 smaller fragment, as well as a young but very perfect example, are in the Museum 

 of Practical Geology ; and there are seven other specimens in Mr. Vicary's Collec- 

 tion, two of which are almost perfect from apex to body-chamber, though they 

 have for the most part lost their outer test. 



Remarks. — Phillips's figure is a not very successful representation of a fine and 



