92 Mr. W. King on certain Genera 



Strophalosia. 



If we examine Productus giganteus, P. horridus, &c, it will 

 be seen that they do not possess articulating condyles nor an 

 area. The absence of these characters has generally been urged 

 as essentially distinguishing Productus from most of the Pal- 

 liobranchiate genera. It is not to be denied, however, that 

 some species of this genus may have existed possessing an area 

 and teeth in a rudimentary or incipient state*. Considering 

 how closely allied Productus is to the dentigerous and areated 

 genera, the presence of these characters under such a condition 

 is to be expected in some species, which in this case would be 

 looked upon as so many aberrant forms ; but when we find both 

 the condyles and area assuming a fully developed form, and pre- 

 vailing in a number of species allied to each other by other di- 

 stinguishing characters; and these species belonging to three 

 consecutive geological periods, and having a wide geographical 

 range, it then becomes a question whether it would not be work- 

 ing out a natural division to group such species under a separate 

 genus : as this is my opinion, I have been induced to form a 

 genus for them, bearing the name Strophalosia. 



It will now be necessary to enter more into detail respecting 

 the distinguishing characters of Strophalosia. Both valves pos- 

 sess an area, that of the ventral valve being merely the hinge-plate 

 thickened : the area of the dorsal valve is furnished with a cica- 

 trized deltidium, at the base of which are situated two condyles 

 which fit into a pair of sockets excavated in the hinge-plate of 

 the opposite valve, one on each side of the cardinal muscular 

 fulcrum : the umbone of the large valve is generally flattened or 

 irregularly indented, and the entire face of the ventral valve is 

 often furnished with spines f. 



Hypothyris only to the extent that Orthis adscendens and Spirifer lietero- 

 clitus do from their respective genera, I would not hesitate to consider them 

 as Hypothyrises. 



* M. Verneuil places Productus comoides in Chonetes, because it possesses 

 an area and cardinal spines. If the figures given by Von Buch in plate 1 

 of his memoir on Productus represent the internal structure of P. comoides, 

 we may then be certain that this species does not belong to Chonetes, since 

 the concave or ventral valve of this genus is not furnished with the crescent- 

 shaped bodies to be seen in one of the figures just referred to, and charac- 

 teristic of Productus. A specimen of Productus giganteus in the Newcastle 

 museum exhibits what might be taken for an area, but which, instead of 

 oeing an additional piece set on the hinge-plate, as is the case with a true 

 area, is only the hinge-plate itself considerably thickened. Perhaps this is 

 the case with the Productus comoides examined by M. Verneuil. 



f M. Verneuil has pointed out the existence of spines on the flat valve of 

 the so-called Productus horrescens. In the true Productuses, the spines, 

 when present on this valve, are generally confined to the cardinal region : 

 Productus punctatus and P. fimbriatus may be exceptions. 



