FROM THE TERTIARY OF VIRGINIA. 261 
Length .08. Breadth .15 of an inch. 
Remarks.—The longitudinal strive 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, &e. 
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 Delphinulew. 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, Pu. 86. Fic. 70. 
D. testd concavd, orbiculari, depressd, supra planulatd, tenut, nitente, sub-striatd; spird brevissimd, obtusa; suturis 
linearibus; anfractibus quatuor, rapide crescentibus, planulatis; strits longitudinalibus, parvis, rarissimis; anfractu 
ultimo sub-angulato; basi striald; wmbilico magno, profundo, intus striato; aperiurd magna, ovald. 
Shell concave, orbicular, depressed, flattened above, thin, shining, sub-striate; spire very short, obtuse; sutures 
linear; whorls four, rapidly increasing, flattened; striw 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. tipara, Pu. 36. Fic. 71. 
D. testé orbiculari, depressd, sub-planulatd, crassiusculd, levi, nitente; spird brevissimd, rotundatd; suturis impressis ; 
anfractibus quinque, convexis, politis; anfractu ultimo rotundato; basi levi; wmbilico latissimo, profundo; apertura 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-stTRiTA, Pr. 36. Fie. 72. 
D. testé orbiculari, depressd, crassd, diaphand, sub-cancellatd; spird brevissimd, ovatd, prope apicem longitudina- 
liter et profundé sulcatd; suturis impressis, linearibus; anfractibus quatuor, convewis; 
suluram inferiorem pene obsoletis; striis oblique transversis, parvis, crebris; 
VOL. IX.—69 
sulculis longitudinalibus, ad 
anfractu ultimo tum carinato tum angu- 
