Maryland Geological Survey 371 



Genus GONIOPHORA Phillips 



Goniophora hamiltonensis Hall 

 Plate XXXIII, Figs. 11-1:5 



Sanguinolites hamiltonensis Hall, 1870, Prelim. Notice Lamelllbranchiata, ii, 

 p. 36. 



Goniophora hamiltonensis S. A. Miller, 1877, Cat. Amer. Pal. Foss., p. 192. 



Goniophora hamiltonensis Hall, 1885, Pal. N. Y., vol. v, pt. i, Lamelllbran- 

 chiata ii, p. 296, pi. xliii, figs. 8-15, 17-21. 



Goniophora hamiltonensis Clarke, 1903, N. Y. State Mus., Bull. 65, p. 390. 



Goniophora hamiltonensis Grabau and Shimer. 1909, N. Am. Index Fossils, 

 vol. i, p. 519, fig. 699c. 



Description. — " Shell large, trapezoidal ; length more than twice the 

 height; basal margin gently cvrving, sometimes nearly straight and 

 slightly affected by the sinus; posterior margin obliquely truncate; an- 

 terior margin concave below the beak and abruptly rounded below; car- 

 dinal line very slightly arcuate, extending for two-thirds the length of 

 the shell. Valves moderately convex below the umbonal ridge, and con- 

 cave above it to the cardinal line; beaks subanterior, small, closely 

 incurved, situated from one-fourth to one-sixth the length of the shell 

 from the anterior margin ; umbonal ridge angular, strongly defined, 

 arching over the beaks and extending in nearly a direct line to the post- 

 basal extremity; umbonal region scarcely gibbous, separated from the 

 anterior end by a broad undefined sinus, which becomes obsolete in some 

 specimens. Test of moderate thickness, marked by regular, prominent, 

 lamellose striae." Hall, 1885. 



A small, exfoliated and somewhat imperfect right valve was found on 

 the road from Hancock to Harrison ville, Penna., which is referred to this 

 species. It has a sharp and prominent umbonal ridge, extending in a 

 direct line from the beak to the post-basal extremity, while the posterior 

 margin is apparently quite truncate, characters which are diagnostic of 

 this species. It resembles quite closely fig. 12, pi. xliii, ii Lamelllbran- 

 chiata, pt. i, vol. V, Pal. N. Y., and similar exfoliated specimens of this 

 species in the New York State Museum. 



Leng-th, 20 mm.; height, 11 mm. 



