310 Proceedings of the Royal Physical Society. 



Productus (?), sp. ind.— PL XIV., figs. 44-49. 



Sp. char. — Ventral valve convex, gibbous, with a slight 

 mesial sinus ; umbo large, projecting a good deal beyond the 

 hinge line, and a little curved downwards ; hinge line straight, 

 scarcely as broad as the shell. Adductor impressions elon- 

 gated, divided by a groove (ridge in the cast), and placed on 

 a central prominence between the two deep depressions form- 

 ing the scars of the adductors. The latter are strongly marked 

 with vertical ridges and grooves. The dorsal valve is flat, or 

 nearly so, and of considerable thickness. In the interior the 

 cardinal process is strong and prominent, projecting vertically 

 above the hinge line; the alar ridges at the base of the cardinal 

 process are strong and thick ; alar angles apparently rounded ; 

 the cardinal process is continued towards the front of the valve 

 into a very well-marked entire septum, extending to within a 

 very short distance of the margin, and terminating in a slight 

 enlargement or button (in the cast this is seen as a groove, and 

 the alar ridges as broad depressions). Adductor impressions 

 rather posterior, dendritic, and extending outwards laterally. 

 Reniform or vascular impressions apparently well marked, 

 their upper margins cutting the septum at about a third from 

 the umbo ; the expanded or terminal portion almost circular, 

 and not large for the size of the valve. In the cast the sur- 

 face of both valves is grooved and pitted, the pits (represent- 

 ing granules in the true shell) are very plentiful in the dorsal 

 valve towards the front margin. External surface of shell 

 not preserved. 



Ohs. — I have already explained (p. 286) the grounds upon 

 which this form has been separated from Prod, hrachythcerus. 

 Professor De Koninck has suggested that it may be referable 

 to Productus fragilis (Dana). Pleased as I am to be able to 

 confirm Professor De Koninck's views on the separation 

 of the two specimens referred by Morris to P. Irachy- 

 thcerus, I most emphatically dissent from his suggestion 

 that the silicified example may be P. fragilis (Dana), for 

 the following reasons : Productus fragilis (Dana), of which 

 De Koninck gives a long description, was so very generally 

 described, and illustrated with such unsatisfactory figures, 



