ANIMALS. 103 



Family Strophomenid^, King, 1846. 



Tliis family of Sarcicobrachial Palliobranchs, as will be seen by a reference to the 

 Synoptical Table, embraces a number of genera, most of which appear to be furnished 

 with slightly distinctive testaceous characters, — as the presence of spines on the hinge — 

 a closed, or an open fissure — some peculiarity in the dental plates — a twisted, or an 

 incurving beak. All the known genera are dentigerous, areagerous, and, with one 

 exception (Chonetes), unprovided with spines -} they are generally characterised with 

 large pallial vessels, which become minutely divided at the margin of the valves. 



Most of the genera were in existence during the earliest organic period, — the Silurian; 

 they gradually decreased in number, however, during those immediately succeeding, 

 particularly the carboniferous ; after which, and to the Jurassic period, they were 

 represented by only a few straggling forms, — concluding from the single known 

 Permian StreptorhyncJms {TerebratuUtes) pelargonatus, the only known (?) Triassic 

 SfreptorJiync/ms {Spirifer) spiirius, Miinster, and the solitary Jurassic Strophomena 

 {Leptcena) Liasina, Davidson. 



Having in some respects modified my views on this family, compared with those 

 given in my paper on the ' Palliobranchiata,' I purpose, before describing the next 

 species, to make a few remarks on the strophomenideal genera of other writers, and 

 those proposed by myself. 



Rafinesque was the first to found a genus for shells belonging to this family. 

 Whether his Strophomena were ever published by himself, or it first appeared under 

 the editorship of some other author, I have not been able to ascertain ; but this is 

 certain, that the genus was described by M. de Blainville, in his ' Manuel de Mala- 

 cologie,' 1825, and afterwards in the ' Dictionnaire des Sciences Naturelles,' t. li, 1827, 

 in both of which it is typified by the American Strophomena rugosa, Raf., which, from its 

 general form, and its large valve being concave, and the opposite one convex, I have 

 little doubt is identical with the recently proposed Strophomena {Leptcena) planumbofia 

 of Hall.^ Bearing in mind the characters of its specific type, it will be necessary to 

 consider the genus Strophomena to comprise such shells as S. alternata, Conrad., 

 S. Butertrii, Murch., S. euglyjjha, Dalman, S. plano-convexa, Hall, and several others, 



1 Schizophoria resupinata appears to have had a tendency to become spiniferous. 



2 Vide Palaeontology of New York, vol. i, p. 112, pi. xxxi B, fig. 4 ; and Bull, de la Soc. Geol. de France, 

 2"' serie, t. v, pi. iv, figs. 3 a, b, c, d. In ray paper on the ' Palliobranchiata,' it is stated that Strophomena 

 rugosa "is evidently closely allied to, and congeneric with, Leptcena alternata ;" Mr. Sharpe gives a more 

 exact account of it as regards form, in stating that the former, " having the dorsal valve concave, limit us to 

 the group of which Orthis umhraculum may serve as the type." (Vide Geol. Jouru.; vol. iv, p. 178.) From 

 a recent examination of the figure in the 'Diet, des Sciences Naturelles,' I have become convinced that 

 Strophomena rugosa has the large valve concave, which is also rendered clear by the following diagnosis : 

 "Coquille bombee en dessous, et dont la valve superieure est un peu concave et chargee de petites stries 

 rayonnantes." (Loc. cit.) 



