34 SYNOPSIS OF THE CHARACTERS OF THE 



Naticopsis PLICISTRIA. Phil. SP. 

 Natica plicistria. Phil. Geol. York. 

 Sp. Ch. — Ovate; spire prominent, of three volutions, slightly concave at the sutures, where they are 

 strongly striated ; surface with fine, oblique striae. 



This is easily distinguished from the N. Phillipsii, by its prominent spire and ovate form ; it is a much 

 scarcer species; the plication of the sutures appears to be the remains of delicate membranaceous plaits, such as 

 we see in many of the Haliotidce. 



Naticopsis sperata. Sow. sp. 



Nerita spirata. Sow. Min. Cou. 

 Sp. C/i.— Globose, obliquely compressed; spire flattened, of three turns ; volutions sharply striated across; 

 strias rising into a sharp plication at the sutures. 



This pretty little species was originally described by Mr. Sowerby as a Nerita ; but from the flattened, 

 smooth, arched, inner lip, it must belong rather to the present genus. The Silurian fossil of this name seems a 

 perfectly distinct species. Diameter ten lines ; length eight lines. 



EUOMPHALUS. Sow. 



Gen. Ch. — Discoid; spire depressed, or elevated, of many slowly increasing whorls ; dextral; whorls entirely 

 exposed by the very large vunbilicus; surface generally smooth, or destitute of spinous processes. 



The genus Skenea of Fleming does not appear to me to difler materially from the previously proposed 

 genus Euomphalus, esTpeciaWj if extended, as Professor Fleming has done, to those fossils; it would be a more 

 definite and better genus if restricted to the recent shells of which the Serpula cornea, Adams, is the type. 

 Cirrus difiers in nothing except that its spire is more or less produced, a character so vague and variable as to 

 be of no use as a generic distinction, and I have therefore rejected Skenea as applied to the fossil species, and 

 mercred Cirrus intoi?H07n;j^aZ?«, knowing of no character by which to distinguish them; at the same time I am 

 perfectly aware that Euomphalus, as it now stands, requires division; thus those species with rounded whorls, 

 and a circular- entire mouth, should obviously be separated from those in which the whorls are angulated, and 

 in which there is a slit in the outer lip, as in Schizostoma. They resemble Lamarck's Delphinula in the de- 

 pression of the spire, its obtuse tip, and the great size of the umbiHcus, as well as in the absence of the pillar ; 

 differing principally in the smoothness of the surface. 



Euomphalus acutus. Sow. sp. 



Cirrus acutus. Sons. Min. Con. — Cirrus acutus. Phil. Geol. York. 



Sp. C/t.— Acutely conical; volutions very convex, with a flat space on the upper part of the lower ones; 

 body whorl much larger than the preceding ones. 



The lower basal turn is almost discoid, closely resembling an Euomphalus pentangulatus in form ; but the 

 whorls from thence to the tip form an acutely conical spire. Diameter one inch six lines ; height one inch three 

 lines ; thickness of last whorl six Hnes. Some specimens from Little Island, Cork, measure tliree inches in dia- 

 meter. 



Euomphalus ^qualis. Sow. sp. 



Planorbis squalis. Sow. Min. Con. — Skenea asqualis. Flem. Brit. Anim. 



Sp. Ch. — Discoid; equally concave on both sides; whorls fully exposed; an obtuse keel on the right 

 side ; left side bicarinatc ; mouth circular. 



This species might, perhaps, be retained imder the genus Skenea, as it appears more nearly allied than 

 any of the other fossil species to the recent Serpula cornea, Adams, and Helix serpuloides, Mont., forming the 

 type of that genus ; it is very local. Diameter six lines. 



