942 MR. T. H. WITHERS OX 



the collection of the Mineralogical Museum of the University of 

 Copenhagen, and Dr. Ravn informs me that this species has been 

 found only in the Upper Senonian (Zone of Scaphites constrictus). 

 Darwin doubtfully referred *S'. (?) cretce to the genus Scalpellum, 

 and observed (1851, p. 45) : " Professor Steenstrup was originally 

 inclined to believe that the capitulum [of S. (?) cretce] was formed 

 of only five valves ; could this be proved, the species would very 

 naturally rank with a small recent one from the Island of 

 Madeira, which, owing to the upward growth of the scuta, and to 

 certain peculiarities in the animal's body, I have felt myself com- 

 pelled to raise to the rank of a genus, under the name Oxi/naspis." 

 An examination of the valves from Copenhagen University, and 

 of some valves obtained by myself from the matrix of a specimen 

 presented to the Geological Department of the British Museum 

 by Copenhagen University, shows, at any rate, that we can no 

 longer hold Steenstrup's view that *S'. (?) credos had only five valves. 

 Among the above valves are some small lower lateral plates, 

 which, although not so well preserved as those from the English 

 Cenomanian Chalk, obviously belong to the same general type as 

 those of Zeugmatolepas mockleri. S. (?) cretcs, together with the 

 species now described, is included, for the reasons previously 

 given, in the new genus Zeugmatolepas. 



The scutum of Z. cretce differs from that of Z. mocHeri in that 

 the umbo is further removed from the apex, being situated almost 

 midway on the occludent margin, and in a greater portion of the 

 valve near the basi-lateral angle being sharply upturned almost at 

 right angles to the middle part of the basal margin. The lateral 

 (or tergal) portion of the valve is not steeply inclined from the 

 umbo, and there is no deep trough, as in Z. mockleri, running 

 parallel with the upper occludent margin. These and other difier- 

 ences result, no doubt, from the difference in position of the umbo, 

 and the consequent greater development of the tergal or lateral 

 portion of the valve. The carina in Z. cretce is relatively wider 

 than in Z. mockleri, the central ridge is much more obscure, and 

 in the tergum there is a much wider groove near the occludent 

 margin. The whole of the valves in Z. cretcp. are appreciably 

 thinner. These differences, however, while deserving of specific 

 distinction, appear to result from the further development of 

 valves like those of Z. mockleri, and consequently I consider these 

 two species to be closely and probably directly related. 



Genus Calantica. 



1825. Calantica Gray, 'Annals of Philosophy' (n. s.), vol. x. 

 p. 101. 



1907. Calantica Gray : Pilsbrv, Bull. U.S. JSTat. Mus. no. 60, 



p. 8. 



1908. Calantica Gray : Pilsbry, Proc. Acad. Kat. Sci. Philadelphia,, 



p. 106. 

 Capitulum with two whorls of ^•alves, the upper comprising 

 paired scuta, terga, and a eaj'ina, the terga occupying the wholo 



