56 G. F. MATTHEW: ILLUSTEATIONS OF 



^"avity. There are two or more septa uoar the apex, and about ten diaphragms in the 

 lateral sheath beside the body cavity ; these diaphragms are directly transverse on the 

 ventral side, but bend toward the apex at their extremities on the dorsal side. 



Striœ on the dorsal side coarser than in the type and strongly arched. Substance of 

 the shell thicker than in the type. 



Operculum unknown. 



Length, about 33 mm. Width, 11 mm. Eate of tapering in the apical half, 1 in li mm. ; 

 in the wider half, 1 in 5 mm. Average tapering of the whole shell, 1 in 2J mm. 



Locality and Horizon. In the purple-streaked sandstones of Div. 1.^-. Hanford Brook, 

 St. Martin's. Frequent. 



VI.— GASTEROPODA. 



STENOTHECA, Hicks. 



This genus was proposed by Dr. Henry Hicks in 1872 to include a minute corrugated 

 shell found in the Menevian group in "Wales. It was described by Dr. Hicks as a "curved 

 shell," " a small wide form with lines of growth strongly marked on its surface." The 

 genus is represented in Div. \.d by several small compressed species, none of which appear 

 to be identical with S. cornucopia, the type of the genus. 



Dr. Hicks placed this genus among the Pteropods,' but if I am right iu referring our 

 shells to his genus, there would seem to be features indicating affinities with the Gastero- 

 pods and Heteropods rather than with the Pteropods, and I have, therefore, placed the St. 

 John species under the Gasteropods. 



The little shells of this genus are always tinequilateral, and usually have a more or 

 less prominent ridge or carina on the back. Among recent molluscs, Carinaria and Atlanta 

 are the forms which appear to come nearest to them ; iu general outline they resemble the 

 shells of the former genus, but their compressed form reminds one of those of the latter ; 

 from both, however, they differ in the straight or nearly straight apex, and in the 

 arrangement of the lines of growth on the shell. All the species are more or less ribbed or 

 thickened along the back, and it seems probable that in one of the species there was a 

 suture along this line, as the sides are sometimes found detached and one side pushed 

 past the other. The apex of two out of the five species of the St. John group is known, 

 and does not show any tendency to a coiled form as in Carinaria, Atlanta, or any other 

 genus of Heteropods with which it may be compared ; among certain genera of Gastero- 

 pods, however, as Dentalium, Parmophorus, and Patella, similar apices may be observed. 



These little Stenothecœ appear to have had thin calcareous shells, and to have been 

 denizens of the open sea and of tranquil bays along the coast, as they are found in the fine 

 shales of Div. \.c and l.d in company with Pteropods and Trilobites. 



Stenotheca Hicksiana, u. sp. (Plate VI. Fig. 14.) 



Subtriangular, with a strongly arched anterior or dorsal margin, and a nearly straight 

 posterior or ventral margin ; the line of the aperture is curved downward in the posterior 



' Quart. Jour. Geol. Soc, May, 1875, p. 192. 



