(87) Galveston Well Fossils 5 



less prominent concentric sculpturing ; ears, especially the anter- 

 ior with radiating costae more or less fimbriately sculptured ; space 

 between the ears and the extreme lateral costae on the side of the 

 valve, smooth and moderately broad : left valve much less inflat- 

 ed ; with 17 or 18 slightl}' narrower and less flattened ribs with 

 broader interspaces strongly marked by concentric striae ; ears 

 nearly equal , radially striate ; space between them and the ex- 

 treme lateral ribs, smooth. 



This species somewhat resembles P. incEqualis Sow\ , from West 

 Indian Miocene deposits. That species, however, is smaller and 

 more oblique. P. dislocatus Say is much less inequivalve and has 

 two or three more costae on each valve ; the spaces too, between the 

 extreme anterior and posterior ribs and the ears are radiately stri- 

 ate or costate. 



Range in depth. - From 2,236 to 2,920 feet. 



MYTILUS. 



Mytilns incrassatus. 



Syn. M. incrassatus Con., Am. Jr. Sci., vol. 41, 1841, p. 347. 

 Con., Foss. Med. Tert., 1845, p. 74, pi. 

 32, fig. 4- 

 Mytiloconcha incrassata Con., Pr. Ac. Nat. Sci. Phila., 

 1862, p. 291. 



I am not aware that Mytili of this general type have appeared 

 on the Atlantic or Gulf slope since late Miocene or early Pliocene 

 times. Forms still living in the Pacific have ponderous shells 

 with thickened hinge area, as for example M. inagellanicus, but 

 none agree quite so well with the Galveston species as incras- 

 satus does. 



Rarige in depth. - From 2,384 to 2,871 feet. 



DREISSENSIA. 



Dreissensia sp. 



This form is very abundant, but generally badly eroded ; differs 

 but little from specimens now living on the coast of Florida. 



Range in depth. - From 2, 123 to 2,873 ^^^t. 



A RCA. 



Area incongrua. 



Syn. A. incongrua Say, Jr. Ac, Nat. Sci. Phila., vol. 2, 1822, 



