﻿310 



GASTEROPODA OF THE INFERIOR OOLITE. 



turriting, and ornamented by spirals decussating with numerous closely set axial 

 lines. In the last three or four whorls of the spire the ornamentation becomes 

 very rugose, but with considerable differences of development. The anterior half 

 of the whorls is occupied by two keels, of which the upper one is grossly tuber- 

 culated ; the lower keel is sometimes tuberculated, sometimes it is little more than 

 a serrated band (as in C. gradatns). Axial ribbing extremely coarse and rather 

 wide apart. In well-preserved specimens a system of reticulation between fine 

 intermediate spirals and the oblique growth-lines may be seen. In specimens 

 from Coker this feature is rarely preserved. 



The bodj^-whorl is largely ventricose, subangular, and rugosely bicarinate, but 

 there are considerable differences ; specimens from Dundry have a rounder and 

 still more ventricose body-whorl, with ornamentation so irregular that the spiral 

 is often overpowered by thick tubercular axial costge. The base is full, sub- 

 angular or rounded, and strongly costated ; the umbilicus varies considerably in 

 width and depth. Aperture circular, expanding somewhat, and adherent. 



Relations and Distribution. — There is a strong temptation to make several 

 species out of Cirrus Leachi, and indeed one might fill a quarto plate with figures 

 of varieties. Firstly, we have — 



a. The very wide angled and coarsely costate form with bicarinate and 

 angular whorls from the bifrons-beds of Compton, which was figured by Moore ; 

 the ornamentation somewhat resembles that of Turbo Hornesi, Stol., but the 

 Compton fossils have a much wider spiral angle, and are umbilicated. 



b. The prevailing form at Coker and elsewhere in the Murchisonx-zone of 

 Dorset is not unlike that of the Compton fossils, but the ornaments are not quite 

 so rugose, and the spire is rather higher. This variety was well figured by 

 J. Buckman. Fig. 3 of the accompanying plate represents a somewhat less 

 angular form of this variety. 



c. There is a smaller and somewhat less ventricose variety with finer and 

 closer costas from Bradford Abbas (see fig. 5). 



d. Specimens from Dundry, in the Bristol Museum, are extremely ventricose, 

 the body-whorl being both wide and high, and the bicarinate character becomes 

 almost obliterated by rugose axial ornamentation. To a certain extent this 

 variety is represented by Cirrus Fourneti, Dum. I am somewhat inclined to 

 classify the very elegant specimen from Bradford Abbas, fig. 4, with this section. 

 In this particular specimen the umbilicus is so restricted that I have distinguished 

 it in my Collection as var. " subumbilicata." 



( 'irrus Leachi abounds at Coker and Stoford, but is not very common at 

 Bradford Abbas. Fine specimens were formerly obtained at Dundry. One 

 would expect some modification of the demoid species of Cirrus to occur in the 

 Cotteswolds, but at present I am without reliable information on this point. 



