PRODUCTUS. 35 



valve being covered by small pits and rugosities. In the interior of the smaller or dorsal 

 valve (fig. 21) the cardinal process is produced beyond the level of the hinge-line, and 

 varies somewhat in shape in different individuals (figs. 21 and 25, as seen from the 

 interior of the valve ; figs. 23 and 24, from the exterior). This boss is bifid at its extremity, 

 with a slit or groove along the middle in each of the lobes facing the exterior of the valve. 

 From the base of this process proceed three ridges or crests ; one on each side runs almost 

 parallel to the hinge-line, and the third forms a central mesial ridge or septum, which, 

 becoming more acute and elevated at its extremity, extends to about two thirds of the 

 length of the valve. On either side of this ridge are situated the muscular and reniform 

 impressions ; those left by the adductor are of a triangular shape, deeply grooved, and 

 more or less elevated above the level of the valve. 



In front of the muscular scars, and about the middle of the valve, are seen two 

 elongated reniform impressions or callosities, bounded by small ridges, which, after 

 dividing the adductors in a perpendicular manner near to the mesial septum, proceed 

 outwardly in an almost horizontal direction, when turning abruptly, form an elongated 

 half circle, which, becoming again horizontal, terminates close to the septum (fig. 21 ; and 

 cast, fig. 19). 1 



Nearly half of the posterior internal surface of the valve unoccupied by the impressions 

 above enumerated is minutely pitted, denoting, in all probability, ovarian spaces, while 

 the remaining portion is covered with a multitude of short spinose tubercles, which become 

 especially visible near the marginal portions of the shell. There is, also, a row of 

 perforations, due to the cardinal spines, between the hinge-line and the upper pair of 

 ridges which depart from the base of the cardinal process. 



material procurable, and in them will be found certain details -which have perhaps not hitherto been as 

 carefully delineated. Professor King's description and figures of this shell in his Monograph are very 

 excellent, but, with the exception of his fig. 10, chiefly relate to differences observable in the external shape ; 

 so that, by combining mine with his, every external and internal feature, I trust, will have been satisfactorily 

 exemplified. 



It must also be observed, that although the adductor impressions in the ventral valve are not so 

 broad as the cardinal ones, they are much more elongated, and placed at variable levels in different 

 examples ; thus their lower extremity does not attain the level of the lower margin of the" cardinal impres- 

 sions, or extends beyond them in either direction. 



1 In his excellent description of the interior of the smaller valve of this Productus, Mr. Howse ob- 

 serves — " It is generally supposed that the reniform callosities are connected with the vascular system, but 

 this supposition appears to be unsupported by a comparison of these processes with the corresponding 

 parts of other Brachiopods. If we compare them, for example, with the same valve of Argiope or of 

 Thecidium, genera which show points of resemblance to this in several particulars, we find that these pro- 

 cesses have served for the attachment of the oral arms ; and this view is supported by all that we know of 

 the position of these arms in both recent and fossil genera, — at least these structures cannot be attributed 

 to the vascular system, or they would undoubtedly be present in both valves, whereas they are confined to 

 one. On some casts of this Productus a great number of small parallel grooves or furrows are seen running 

 from the central ovarian region to the anterior margins of the valves ; they are not very distinct, but 



