354 THE PALEONTOLOGY OF MINNESOTA. 



[Ltngnlwma galenensli. 



Trimerellidw. We do not regard these genera, however, as in the direct line of 

 development towards Trimerella, but rather as a branch from Lingula, probably 

 having its origin during Trenton times, and terminating with the Niagara forma- 

 tion. In the Black River group, at Pauquette Rapids of the Ottawa river, in 

 Canada, we find Obolus canadensis, and 0. magnificus Billings. These species Billings 

 subsequently referred to his genus Obolellina, now regarded as synonymous with 

 Dinobolus, Hall. In the Galena formation of Wisconsin and Minnesota, there is 

 another form related to the above species, Dinobolus parvus Whitfield. These species 

 were in all probability derived from Obolella, while Monomerella and Trimerella had 

 their origin in Dinobolus. If this opinion is the proper one, Lingulops and Lingulasma 

 should be separated from the Lingulidce and Trimerellidce, and referred to a new 

 family, the Lingulasmatidce. This family will then follow the Lingulidce. 



LINGULASMA GALENENSIS. 



PLATE XXX, FIGS. 1-4. 



1892, April 1. Lingulasma galenensis W. and S. American Geologist, vol. ix, p. 285. 



Shell large, oblong, subpentagonal. Anterior margin slightly convex, and 

 somev/hat produced in the center; anterior angles narrowly rounded; lateral margins 

 straight, nearly parallel, rounding rapidly into the more or less convex postero- 

 lateral margins. Ventral beak somewhat extended beyond that of the dorsal valve. 

 Valves strongly convex, dorsal more than the ventral; point of greatest convexity, in 

 the former at one-third the entire length of the valve from the posterior margin, 

 in the latter nearly central. Surface of each valve with three slopes in the anterior 

 half; the central one flat or very slightly convex, with two broad and shallow depres- 

 ssions, causing a small central extension of the anterior margin; lateral sides very 

 rapidly descending and somewhat convex. Surface concentrically striated; at irregu- 

 lar intervals the striae rise into small pointed pustules radially arranged. These 

 radial series of granulations are most prominent on the flattened, central, anterior 

 portion of the valves; thirteen to fifteen of them in 5 mm., while twenty-eight 

 pustules occupy the same length, measuring along a series. 



Interior of ventral valve with a diamond-shaped concavo-convex platform, 

 strongly elevated, and excavated anteriorly. Posterior margin of the specimen 

 slightly broken; an internal arched deltidium not present. Umbonal scar(</) close 

 to the posterior broken edge, and upon each side of it is a diverging excavated ridge. 

 In front of the umbonal scar, and occupying the lateral portions of the platform, 

 are the progressive tracks of the lateral (I) scars. At the posterior end of the plat- 

 form are two slightly diverging, linear depressions, which terminate near the mid- 

 length of the platform; and here originate two linear and parallel median elevations. 



