subcarboniferous period. 85 



Family STROPHOMENID^. 



Genus STROPHOMENA Rafluesque, 1827. 



Strophomena rhomboidalis Wilckiiis, * aj). 



Plate V, Ug. 5. 



ConcMta rhomboidalis Wilckins, 17G7, Nacbricht von selt. Verst., 77. 



Anomites rhomboidalis Wahlenberg, 1821, Acta Societat. Scieut. Upsal. viii, 05. 



Froductiis depressa Sowerby, 1823, Mineral Concbology, v, 80. 



Lcpiaina rtigosa Dalnian, 1820, K'nigliga Vetens. Akad. Haiidl., 100. 



Leptwna tenuistriatn Sowerby, 1839, Silurian System, 023, 030. 



Strophomena depressa Vauuxem, 1842, Geol. Third District New York, 79. 



Orthis depressa Portlock, 1843, Geol. Loud., Tyrone, & Ferm., 450. 



Lepttena temiistriaia Hall, 1847, Paleontology of New York, i, 108. 



Strophomena rhomboidalis Lindstrom, 1800, Gotbl. Brach., 371. 



Strophomena rhomboidalis Hall, 1807, Paleontology of New York, iv, 70. 



Strophomena rhomboidalis Davidson, 1808, Trans. Geol. Soc. Glasgow, Paleoz. Ser., i, 10. 



Strophomena rhomboidalis Meek and AVortben, 1808, Geol. Surv. Illinois, iii, 420. 



Strophomena rhomboidalis Meek, 1873, Paleontology of Obio, i, 74. 



Shell varying in outline, but generally subsemicircular, widest at the 

 hinge-line; lateral and front margins bent strongly upward all around, 

 the portion inclosed by the geniculated margin flattened in both valves ; 

 the surfaces of these flattened spaces marked by conspicuous concentric 

 wrinkles that increase in size from the beak outward; area narrow in both 

 valves, that of the ventral being a little wider than the other. Surface 

 marked by fine radiating striae, which are nearly unifonu in size, close -set, 

 increasing both by implantation and bifurcation, most frequently by the 

 latter method on the ventral valve and by the former method on the dorsal. 

 Under a lens, minute concentric striae are usually to be seen, as is also 

 the punctate structure of the test, upon exfoliated surfaces. 



Breadth &t the hinge-line, of the largest specimen contained in the 

 collections, four and a half centimeters. They are often smaller than this, 

 their proportions and outline being also very variable. 



The geological range of this species is greater than that of any other 



* This is one of the most widely known of all the species of fossil Mollunca, and l)y some of 

 its varieties it is familiar to every geologist and collector. Mr. Davidson, in his well-known Monographs 

 gives a large number of authorities who have written npon or noticed the species. The synonymy here 

 given is selected for the purpose of indicating some of the principal points in its literary, history and to 

 show the numerous generic assignments that have been made of it besides the various siiecific names it 

 has borne. 



