SEDGWICKIA. 277 



Genus — Sedgwickia, M'Coy, 1844. 



Synonyms : 



Sedgwickia, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 61. 

 Dolabka (pars), M'Coy, 1844. Ibid., p. 66. 

 Ltonsia (pars), d'Orbigny, 1850. Prodrome de pale'ont., p. 128. 

 Sedgwickia, Morris, 1854. Cat. Brit. Foss., p. 224. 



— ? (Sanguinolites), Meek and Worthen, 1865. Proc. Acad. Nat. Sci. 



Philad., p. 251. 



— Meek and Hay den, 1865. Pal. of the Upper Missouri, Smithsonian 



Cont. Knowledge, p. 38. 



— (Sanguinolites ?), Meek and Worthen, 1868. Pal. of Illinois, 



vol. iii, p. 537. 



— ?, Hall and Whitfield, 1872. Pal. Ohio, vol. ii, p. 89. 



— Bigsby, 1878. Thesaurus Devonico-Carboniferus, p. 310. 



— Etheridge, 1888. Brit. Foss., pt. 1, Palaeozoic, p. 290. 



— Miller, 1889. N. Amer. Geol. and Pal., p. 511. 



Generic Characters. — Shell equivalve, inequilateral, more or less ovate and 

 gibbose. The anterior end is rounded, the posterior obliquely subtruncate, 

 unibones pointed and raised, dorsal slope much compressed and broad. Hinge 

 edentulous, or with a single small cardinal tooth in the left valve. Muscle- 

 impressions very faint; pallial line entire. Surface ornamented by regular, 

 well-marked, concentric small ridges in the anterior part, which gradually become 

 obsolete, so that the posterior two thirds of the valve is smooth. 



Observations. — The genus was founded by M'Coy, who described and figured 

 six species, two of which I am able to retain, but unfortunately the types of the 

 others are not preserved or are too fragmentary for identification. To these 

 must be added Venus centralis, M'Coy, and Dolabra securiformis, M'Coy, which 

 doubtless belong to the genus ; unfortunately, however, the type specimen of the 

 former has decomposed, and that name can no longer be retained, and the latter 

 is evidently the interior of S. gigantea. 



M'Coy says, " The genus Sedgwickia (M'Coy) is composed of a very elegant 

 little group of shells, having analogies which place them, as it were, between the 

 so-called Gypricardise of the older strata, the Axini (Sow.), and the Leptodomi 

 (M'Coy)." " 



The genus Schizodus, to which the Axini are now referred, certainly has a 

 very close resemblance to Sedgwickia, but the latter genus is distinguished by its 

 characteristic surface-markings, the edentulous hinge or single small cardinal tooth, 

 smaller degree of obliquity, and the fact that the umbones are not at all proso- 

 gyrous. 



I have pointed out antea, p. 228, the unsatisfactory nature of M'Coy's genus 



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