168 DR G. W. LEE ON 



Genus Productus J. Sowerby. 



Productus giganteus (Martin). 



The materials are fragmentary, but enough is at hand to show that more than one 

 form may be represented. 



(I) A specimen which when complete must have measured about 15 cm. in width 

 has the type of ribbing and the furrowed surface characteristic of the British examples 

 figured by Davidson, pi. xxxviii. and xxxix. (loc. cit.). (2) A specimen about 12 cm. wide 

 and very transverse, the surface of which is not furrowed, has the ribs separated by wider 

 sulci than in the above. (3) A very large specimen, about 15 cm. wide, is less transverse 

 than the two others, and has finer and more close-set ribs ; its surface is not furrowed. 

 (4) Three small specimens have the Edelburgensis type of ornamentation. 



These four forms are too poorly represented to enable one to say whether they 

 belong to distinct varieties (or species ?) or are but the different growth-stages of one 

 and the same species. 



Productus antiquatus J. Sowerby. 

 Mineral Conchology, pi. 317, figs. 5-6. 



The collection contains a large specimen, 7 cm. in width, agreeing very well with 

 J. Sowerby's figure. 



This form and the following I cite separately, but without expressing an opinion as 

 to their relationship to the Productus semireticulatus of authors. Speaking of the 

 latter, Professor Tschernyschew has made the interesting remark that the flatness of 

 its dorsal valve is a good criterion for distinguishing it from certain species of the group 

 of Productus boliviensis d'Orbigny, to which it often bears some resemblance. 



Productus concinnus J. Sowerby. (PI. II. fig. 33.) 

 Mineral Conchology, pi. 318, fig. 1. 



A strongly geniculated brachial valve seems referable to this species, the main 

 characters of which are well exhibited, with this difference, that in the frontal portion 

 the ribs are separated by wider sulci than appears to be the case in the British form ; 

 but this may be an age-character, this being a large specimen 30 mm. in width. 



Productus longispinus J. Sowerby. (PI. II. fig. 31.) 



Davidson, loc. cit, pi. xxxv. figs. 5 and 12. 



The numerous specimens at hand belong to the slightly transverse, evenly convex 

 type as figured by Davidson, fig. 5 (loc. cit.). One specimen only shows a slight con- 

 vergence towards the lobate form. I have not been able to ascertain whether they 

 possess the " niarginifera" ridge usually present in this species. 



