ANIMALS. 103 
Family STROPHOMENIDA, King, 1846. 
This 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 spmes:' 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 strageling forms,—concluding from the single known 
Permian Streptorhynchus (Terebratulites) pelargonatus, the only known (?) Triassic 
Streptorhynchus (Spirifer) spurius, Minster, and the solitary Jurassic Strophomena 
(Leptena)’ 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 (Leptena) planumbona 
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 &. a/ternata, Conrad., 
S. Dutertru, Murch., S. euglypha, Dalman, 8. plano-convexa, Hall, and several others, 
! Schizophoria resupinata appears to have had a tendency to become spiniferous. 
2 Vide Paleontology of New York, vol. i, p. 112, pl. xxxi B, fig. 4; and Bull. de la Soc. Géol. de France, 
27° serie, te, Vapi, igs. diay 6.¢,)d. In my paper on the ‘ Palliobranchiata,’ it is stated that Strophomena 
rugosa “is evidently closely allied to, and congeneric with, Leptena 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 umbraculum may serve as the type.’’ (Vide Geol. Journ.; vol. iv, p. 178.) From 
a recent examination of the figure in the ‘Dict. 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 bombée en dessous, et dont la valve supérieure est un peu concave et chargée de petites stries 
rayonnantes.”’ (Loc. cit.) 
