398 J. Star Me Gardner — On Cretaceous Aporrhaidce. 



Dimorphosoma calcarata, Sby. Blackdown beds. PL V. Figs. 

 7, 7a, 15, 15a ; PI. XII. Figs. 9, 9a, 10, 11, 12, 12a, 126. 



Shell elongated, slightly pupaeform ; whorls 7 or 8, rounded but 

 slightly flattened ; keels totally obscured by ribbing, except on the 

 dorsal side of the last whorl and on the apex ; ribs oblique, flexuous, 

 thick and regular, with a tendency to form varices, 17 or 18 on the 

 penultimate whorl; apex minute, obtuse with rounded, smooth whorls, 

 carinated at their base. Body-whorl distinctly striated, with a strong 

 rounded posterior keel and subordinate anterior keel, one of the 

 striee below the anterior keel being more prominent than the rest ; 

 no ribs on the dorsal, but ribbed on the ventral side. The principal 

 keel is continued on to the wing in the form of a ridge ending in a 

 sharp point. The wing is simple and more expanded than in the 

 other associated Blackdown species, projected at first at right angles 

 to the axis of the spire, and then curving rather abruptly upward, 

 terminates in a point three- fourths of the height of the spire; margin 

 entire, region above the rib narrow and thickened. Outer lip ex- 

 panded into the wing, thickened internally into a second triangular 

 spoon-shaped lip, smooth ; inner lip thick ; aperture narrow ; canal 

 short. 



This species is that originally described by Sowerby. Its history 

 is given at page 129 of this Magazine. It is found at Blackdown. 

 Mr. Meyer, who has kindly given me the opportunity of examining 

 the many hundreds of specimens in his collection, informs me that 

 this shell is about five times more numerous than that next described, 

 with which it is found associated. It is just possible that this may 

 be the male, and D. neglecta the female, as in Fusus, an allied family. 

 Mr. Gwyn Jeffreys remarks : " Of many hundreds of specimens 

 which I have examined, the males were more numerous than the 

 females." 1 



Dimorphosoma neglecta, Tate. Blackdown. PI. V. Figs. 8, 8a, 9, 16 ; 

 PL XII. Figs. 13, 13a, 14, 15. 



Shell resembling in form that of the species last described ; whorls 

 7 or 8, ventricose, slightly angulate, keels visible on all except those 

 near the apex ; region above the keel nearly smooth or with spiral 

 lines ; that below marked by fine straight oblique ribs, which do not 

 quite reach to the suture, but impress the median keel; they are 

 crossed by 3 or 4 strong striae, and there are 2 or 3 more striae nearer 

 the suture. The number of these spiral striae and the prominence 

 of the ribbing are most variable, the ribs being sometimes scarcely 

 present, but generally most strongly deA^eloped on the penultimate 

 whorl; they may usually be seen on the dorsal side of the last whorl 

 in the form of small oblique tuberculations crossing the keel. The 

 wing is at first constricted, notched, with a single tooth in the notch, 

 and then expanded and curved upward — never having the triangulate 

 inner thickening ; in one specimen figured, PL V. Fig. 10, it is 

 bifurcate. 



1 J. G. Jeffreys, vol. iv. p. 337. 



