INVERTEBRATES. 159 



to the E. discoris group, whether we view these shells as constituting a section 

 of the genus Straparollus, or as an entirely distinct genus. 



A marked subgenus, apparently of this group, from the Carboniferous rocks 

 of California, was described by one of the writers (F. B. M.) under the name 

 Omphalotrochus, in volume 1 of the Palaeontology of that State, p. 15, and fig- 

 ured on pi. 2, fig. 8, 8 a, of the same report. It is a large, very ponderous 

 shell, having much the form of a depressed Pleurotomaria, with a deep, conical 

 umbilicus, and whorls flattened and biangular around the outer side. Another 

 species of the same type was described by d' Orbigny, from the Carboniferous 

 rocks of Bolivia, under the name Solarium antiquum. (See Voyages dans 

 V Amerique Merid., p. 42, pi. 3, Jigs. 1, 3.) 



Straparollus lens, Hall, (sp). 



PI. 14, Fig. la, lb. 

 Euomphalus lens, Hall, Dec, 1860. Thirteenth Ann. Rept. Regents Univ. N.Y., p. 109. 



Shell rather under medium size, lenticular; spire much de- 

 pressed, or rising little above the body whorl; volutions about 

 four, increasing moderately in size, nearly flat, with an out- 

 ward slope above — the slope being about coincident with that 

 of the spire — last one angular around the periphery, and 

 rather distinctly convex and rounded below; suture (in casts 

 at least) well denned ; umbilicus deep, less than the breadth 

 of the outer whorl at the aperture. Surface unknown. Aper- 

 ture transversely subovate, or subrhombic in outline. Height 

 of one of the largest specimens, 0.35 inch ; greatest breadth, 

 0.60 inch; height of aperture, .0.19 inch ; breadth of aperture, 

 0.25 inch. 



The only specimens of this species we have seen not being in a condition to 

 show the nature of the lip, or the surface lines of growth, it is diflicult to de- 

 termine, very satisfactorily, its generic relations. It has the form of some of 

 the lenticular species of Pleurotomaria, but there are no evidences manifest, in 

 any of the specimens we have examined, of a spiral band, as in that genus; 

 hence it seems to belong to a palaeozoic group of lenticular forms, usually refer- 

 red to Euomphalus, as that name is generally used in its widest signification. 

 It is not a typical Euamphalus, however, and if falling within the genus Strap- 



