FROM THE TERTIARY OF VIRGINIA. 261 



Length .08. Breadth .15 of an inch. 



Remarks. The longitudinal strise are so minute as to escape observation, unless as- 

 sisted by a powerful microscope. They do not cross the ribs. The mouth is smooth 

 within, and almost exactly round, except at its junction with the preceding whorl, where 

 there is a small channel. 



This shell bears some resemblance to the Turbo lineatus, Lea, but is separated from 

 that shell by its entire mouth, larger umbilicus, &c. 



I have felt some doubt in placing this and two or three of the following shells in the 

 genus Delphinula. Their general appearance would seem rather to make them ap- 

 proach the Turbo, but their entire mouths constitute them true Delphinulce. The genus 

 Skenea, Fleming, seems well fitted to receive them, but it is described as having the 

 "aperture dilated," a character which is wanting in the shells at present under consi- 

 deration. 



D. CONCAVA, PL. 36. FIG. 70. 



D. testa concavd, orbiculari, depressd, supra planulatd, tenui, nitente, sub-striatd; spird brevissimd, obtusd; suturis 

 linearibus; anfractibus quatuor, rapide crescentibus, planulatis; striis longitudinalibus, parvis, rarissimis; anfractu 

 ultimo sub-angulato; basi striatd; umbilico magno, profundo, intus striato; aperturd magnd, ovatd. 



Shell concave, orbicular, depressed, flattened above, thin, shining, sub-striate; spire very short, obtuse; sutures 

 linear; -whorls four, rapidly increasing, flattened; striae longitudinal, very few, small; last whorl somewhat angular; 

 base striate; umbilicus large, deep, striate within; mouth large, ovate. 



Length .08. Breadth .20 of an inch. 



Remarks. The umbilicus is wide and open, exposing the spire, nearly to the apex. 

 The lines of growth are very infrequent and irregular, both as to size and direction. 



This little shell has no very decided character, and yet it cannot be placed with any 

 species hitherto described. Its nearest analogue is the recent Planorbis parvus, Say, 

 which it much resembles in general outline. 



D. LIPARA, PL. 36. FIG. 71. 



D. testa orbiculari^ depressd, sub-planulatd, crassiusculd, leevi, nitente; spird brevissimd, rotundatd; suturis impressis; 

 anfractibus quinque, convexis, politis; anfractu ultimo rotundato; basi lam; umbilico latissimo, profundo; aperturd rotunda. 



Shell orbicular, depressed, somewhat flattened, rather thick, smooth, shining; spire very short, rounded; sutures 

 impressed; whorls five, convex, polished; last whorl rounded; base smooth; umbilicus very wide, deep; mouth round. 



Length .05. Breadth .10 of an inch. 



Remarks. In this shell the umbilicus is wider than in most of those herein described. 

 The mouth is small and very nearly round. The surface has a very high polish, and a 

 somewhat greasy look. 



This species is very much like the Skenea depressa, a recent shell from the coast 

 of England, but it is much larger, and differs in the shape of the aperture. 



D. OBLIQUE-STRIATA, PL. 36. FlG. 72. 



D. testa orbicularly depressd, crassd, diaphand, sub-cancellatd; spird brevissimd, ovatd } prope apicem longitudina- 

 liter et profunde sulcatd; suturis impressis, linearibus; anfractibus quatuor, convexis; sulculis longitudinalibus, ad 

 suturam inferiorem pene obsoletis; striis oblique transversis, parvis, crebris; anfractu ultimo turn carinato turn angu- 



VOL. ix. 69 



