388 JV. H. Hudleston — Gasteropoda of the Portland EocJis. 



shell, and preserves the angular outline of the rest of the spire. 

 The second or median keel divides it somewhat imequally. Tliis 

 keel, though probably less tuberculated, was more prominent than 

 the upper one : below it the body-whorl tapers rapidly towards the 

 anterior margin. The aperture is wide and semi-ovate, without 

 much excavation of the columella, which was covered by a callus 

 of some extent. The only trace of an umbilicus is a slight groove 

 towards the base of the columella. 



The ornaments of this fine shell were doubtless more prominent 

 originally. The tuberculations have been softened down, and all 

 traces of finer lines, if any such existed, have been removed. The 

 whole appearance of the fossil indicates that it has suffered from a 

 sort of solvent action, and the anterior portion is not sufficiently well 

 preserved to show the notch. 



Helations and Distribution. — If it be admitted that the shell above 

 described is entitled to be ranked in the subgenus of Purpura called 

 Purpuroidea by Lycett, it is, according to our present knowledge, 

 the only representative of the Purpuroids in the uppermost Jurassic 

 rocks. The group has not hitherto been known either in England 

 or on the Continent on a higher horizon than the Coral Eag. As 

 might be anticipated, the nearest allied forms appear to be those of 

 the P. nodulata group. The proportions of Young and Bird's species 

 are nearly the same as in this case, but the contour of the whorls 

 differs materially, perhaps fully as much as does the ornamentation. 

 On the other hand, some persons might be disposed to erect Purpu- 

 roidea Portlandica, Pseudomelania percincta, Natica rugosa and even 

 Natica incisa into a genus having Naticoid affinities, but which 

 possess also other characters which can scarcely be reconciled with 

 those of Natica. If Purpuroidea Portlandica should ultimately be 

 shown to have an anterior groove, it must be removed from the other 

 three, whose apertures are certainly entire anteriorly. 



The specimen now figured was found most probably in the " creamy 

 limestones " of Mr. Blake's classification, and is at present unique as 

 a shell. Nevertheless it is extremely probable that this is the external 

 form oi Buccinum angulatum., which Sowerby describes as "fusiform, 

 short ; sides of spire straight ; the last whorl has one keel in the 

 middle; aperture rhomboidal with a short rounded beak." The 

 small amount of slope in the sides of the spire is very characteristic 

 of P. Portlandica, and the median keel is another connecting feature. 

 It should be noted that in the specimen from Ashendon a portion of 

 the shell is broken away near this keel, so as to disclose the cast, and 

 we at once observe that the mark of the keel in the cast is not at all 

 equal to the prominence of that on the shell. This disposes of the 

 possible objection that the keel of P. Portlandica was much too strong 

 for the cast with which it is sought to identify it. 



Buccinum angulatum is pretty common in the Eoche of Portland, 

 and has been noted in the uppermost Portland stone of Swindon. 

 Should it turn out to be the cast of the species above described, P. 

 Portlandica becomes P. angulata, Sow., and its distribution coincident 

 with that hitherto ascribed to Buccimmi angulatum. 



