242 C. E. Beecher — JY. A. Species of Strophalosia. 



following species yield more positive evidence : Crania radi- 

 cans Winchell* and Aulosteges spoiidyliforrnis White and St. 

 John.f 



The first is here illustrated by figures 14-17, Plate IX, and 

 is seen to agree with typical Strophalosia in every essential 

 feature. The second (Aulosteaes spondyliformis), from the 

 Upper Coal Measures of Iowa, in many respects, resembles the 

 species here described from the Keokuk, but in general form 

 it is more like the European Permian types. The authors 

 give the accompanying description, which well expresses the 

 characters in accord with Strophalosia. 



" Shell minute, parasitic, subtriangular in outline, greatest 

 width near the front margin; posterior half of the lateral 

 margins straight; front broadly rounded, and slightly emar- 

 ginate. Ventral valve not very deep, attached to foreign 

 objects by its spines, which are numerous and rather long; 

 area not quite so high as wide, retreating from the hinge line 

 towards the beak ; pseudodeltidium small and not very promi- 

 nent." 



" Dorsal valve slightly concave, a little more so toward the 

 front margin ; surface marked by somewhat prominent con- 

 centric lines of growth, having always fewer spines than that 

 of the ventral valve, and sometimes none." 



The number of spines shown in the specimen figured by 

 them is eleven, and attention is called to the fact that the 

 specimens were found attached to Ohwtetes and Campophyllum. 



From present information, therefore, the genus Strophalosia 

 may be considered as having the following American species, 

 some of which, however, are doubtfully included. 



Strophalosia radicans Winch ell. Hamilton group. 

 Strophalosia productoides Murchison. Hamilton group. 

 Strop>halosia scintilla Beecher. Choteau limestone. 

 Strophalosia Keokuk Beecher. Keokuk group. 

 Strophalosia spondyliformis White and St. John. Upper 



Coal Measures. 

 Strophalosia truncata Hall. Marcellus shale. 

 Strophalosia f muricata Hall. Chemung group. 

 Strophalosia f nummulina Winchell. Marshall group. 

 Strophalosia ? Guadalupensis Shumard. Permian. 



Several original illustrations of typical Permian species are 

 introduced on Plate IX for the purpose of comparison both 

 with the American Strophalosia, and with the genus Leptw- 

 nisca. 



* Rept. Lower Peninsula Mich., p. 92, 1866. 

 + Trans. Chicago Acad. Sci., vol. i, p. 118, 1868. 



