LAMELLIBEANCHIATA OF THE LOWER IMAKLS. 113 



of the shell as it occurred in New Jersey was considerablv different from 

 those found in the more southern localities (Prairie Bluff, Alabama, and 

 Texas), and usually referred to the same species with the casts from New 

 Jersey. This specimen shows that the shell was considerably extended 

 posteriorly, and also that there was a proportionately wide postero-cardinal 

 area over which the radiating ribs did not extend, and which was separated 

 from the body of the shell by a slight fui-row, forming an area or corslet, 

 as in most species of the genus. The radiating ribs on the posterior third 

 of the shell are very oblique and very much smaller than the others, with 

 shallow interspaces. Area marked by concentric lines only, which are 

 much stronger here than on the body of the shell; crests of the ribs ob- 

 scurely tuberculated on the anterior and median parts of the shell. 



The species differs from T. tlioracica Morton, as figured in his Synopsis, 

 PI. XV, Fig. 1 3, from a specimen retaining the shell found at Prairie Bluff, 

 Ala., in the existence of the a.rea or corslet bordering the posterior hinge- 

 line as well as in the extended posterior extremity, and, notwithstanding tlie 

 great similarity of the internal casts, has been very distinct externallj^ when 

 entire. In consequence of this difference it becomes necessary to separate 

 the New Jersey species under a new name. As the name tlioracica was 

 applied to and illustrated by specimens from Alabama, it will have to be 

 retained for that shell. 



Formation and localities. — It has been observed in the Lower Green 

 Marls at Freehold, Burlington, Monmouth, Holmdel, and other localities in 

 New Jersey as internal casts. The external impression from which Fig. 6, 

 PI. XIV, is taken is from near Holmdel, and was collected by the Rev. 

 Dr. Riley. 



Trigonia Eufaulensis. 

 Plate XIV, Figs. 1-4. 



Trigonia Enfalensis Gabb. J. A. :N^. Sci., Phil., Vol. IV, K S., p. 396, PI. LXVIII, Fig. 

 32. Synopsis, p. 177. Meek, Cbeck-list,p.9. Geol. Surv. N. J., 1868, p. 725. 



Mr. Gabb's description of this species is as follows: " Subtriangular, 



resembling T. alcpformis Sow., in outline, not quite so elongated anteriorly; 



beaks jiosterior; lunule distinct; surface marked by about fourteen ribs, the 



more anterior of which joroceed from the lunule anteriorly and then cross 



4418 MON 9 8 



