142 GASTEROPODA OF THE INFERIOR OOLITE. 



ments consist of stout costas distributed at wide intervals in the form of varices, 

 not usually in alignment, chiefly on the posterior area of each whorl, and very 

 nodose in passing over the keels. Below the keels one, and sometimes two strong 

 spiral bands may be noted, almost giving the appearance of bicarination ; the lesser 

 spirals are fine and numerous throughout the shell. 



The Ponton variety presents the most interest, since here alone have I been 

 able to find a specimen with the wing developed (or preserved), fig. 8 b. 

 Length . . . . .22 mm. 



Width of body- whorl to height of shell . 45 : 100. 



Spiral angle about .... 30°. 

 Probable number of whorls seven or eight. Ornamentation of the spire-whorls 

 as already described. Body- whorl tumid, sub-bicarinate, with two or three coarse 

 nodular varices, and traces of numerous diverging spiral lines. Wing wide and 

 short, and enveloping nearly half of the penult, apparently without digitation- 

 Aperture wide and subquadrate, with an expanding lip, anterior margin slightly 

 excavated ; columella curved and but slightly encrusted ; canal apparently almost 

 as short as in Bracliytrema. 



The Weldon variety, which is presumed to be an immature form, and which 

 might almost be regarded as a distinct species, is most characteristically repre- 

 sented by fig. 8' a, a well-preserved specimen of the more usual form. See also 

 PI. II, figs. 10 a, 10 b. 



Length ..... 10 — 12 mm. 



Width of body -whorl to height of shell . . 55 : 100. 



Spiral angle about .... 40°. 

 A wide-angled, stumpy little shell of about six whorls. Body-whorl tumid, 

 sub-bicarinate, spirally striated, and carrying three or four varices. There is no 

 wing. Aperture wide, with a simple lip, and very short anterior canal, almost 

 like Brachytrema. 



A sub-variety of the Weldon fossil is shown in fig. 8' b. 



Probable length . . . .14 mm 



Width of body whorl to height of shell . . 42 : 100. 



Spiral angle about . . • . 30 . 



Probable number of whorls six or seven ; ornamentation similar to the last upon 

 a narrower and more turrited spire. Body- whorl keeled and spirally ornamented, 

 but entirely without varices. Other indications wanting. This is rare. 



Relations and Distribution. — Accepting the adult specimen from Great Ponton 

 (fig. 8 b), for the moment, as the type of the group, there is nothing like this known 

 from the Inferior Oolite of the other districts. The form of the wing and the 

 character of the aperture remind us of certain specimens of Alaria (Diartema) 

 paradoxa, M. & L., a well-known fossil of the Great Oolite, but the spire is very 



