DUNLET GASTEEOPODA. 43 



PLEUROTOMARIA. SULCATA, Sowerby. 



1819 Trochus sulcatus, Sowerby, Min. Concli., pi. 220, 

 fig. 3 (Pleurotomaria in Index) 

 non Deslongchamps. 



Height 24 mm. Greatest breadth, 30 mm 



The original specimen of the Min. Conch, is in our Musenm. 



"We quite agree with D'Orbigny that P. sulcata^ Desl., is a 

 distinct species (= P. unisulcata, D'Orb.) 



Sowerby' s figures are sufficient to distinguish it from other 

 Dundry forms. 



The whorls are convex but not angular ; the younger ones have 

 fine transverse costse, and the older ones faint transverse lines 

 curved in opposite directions above and below the sinus-band; 

 there are faint longitudinal lines, specially below the suture. 

 Sinus-band not in the middle, but about one-third from the lower 

 suture, and generally forming a concave depression ; it is crossed 

 by curved lines. Umbilicus pretty wide. The outline of the 

 shell is too curved and convex to allow of a definite angle being 

 taken. 



There are eight specimens in the Museum. 



Locality — Dundry. Inf. Ool. 



Professor Quenstedt (Jura., p. 404) suggests that P. Ajax^ 

 D'Orb., may perhaps belong here. I cannot agree with him. It 

 may be wearisome, as he says, to have to determine imperfect 

 specimens ; but the attention which D'Orbigny paid to this genus 

 has resulted, I think, in proving the fact, that it was one 

 extraordinarily prolific in species, and that the differential 

 characters were constant over a considerable area. It is much to 

 be regretted that the Suabian specimens are not more perfectly 

 preserved, for we might then have had proofs of forms inter- 

 mediate between, and linking together, some of D'Orbigny' s 

 species; but imperfect specimens can scarcely invalidate the 

 determinations of the latter. 



