FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 103 



Genus Nucleospira. Han. 



Nucleospira, Hall. Pal. N. Y., Vol. III., page 2191869. 



Etymology: nucleus, a kernel; spira, a spire, alluding to the internal spire of these shells. 



Shell spheroidal or transversely elliptical, more or less gibbous or ventricose, 

 furnished with internal spires, as in Spirifer. Hinge-line shorter than width 

 of shell ; cardinal extremities rounded. Valves sub-equal, articulating by 

 teeth and sockets. Ventral beak extended beyond the dorsal, and beneath it 

 a triangular depression or area, which sometimes terminates in a shallow, 

 spoon-shaped pit, on each side of which, at the base, is a strong tooth. A 

 narrow ridge or septum extends along the center of inner side of valve from 

 beak to base. 



Dorsal valve furnished with a strong, spatulate, cardinal process, which, 

 rising vertically from cardinal margin, is closely grasped at its base by the car- 

 dinal teeth of other valve, and thence bending abruptly upwards, and expand- 

 ing, is projected into the cavity of other beak, lying close upon under side of 

 false area. This process is grooved or depressed in the center of the upper 

 side, so as to leave between it and the arch of the ventral beak a narrow space 

 for the passage of a pedicle, for protrusion of which a minute foramen is 

 sometimes observed in beak. From the sides of this process, above the junc- 

 tion of teeth of other valve, and at the point where it bends upward, originate 

 the brachial processes, which support the spires. A deep cavity beneath the 

 cardinal process extends to dorsal beak, from which originates a thin elevated 

 septum, running to base of shell. Muscular imprints confined to a narrow, 

 oval space. Surface smooth ; shell structure punctate, and, when perfect, 

 covered with minute hair- like spines. 



Nucleospira concinna. HALL. 



Plate XXXII., figures 1, 2, 3 and 4. 



Atrypa concinna, Hall. Geol. Rep/4th Dist. of N. Y., p. 2001843. 

 Nucleospira concinna, Hall. Twelfth Rep. on St. Cab., p. 25 1859. 

 Nucleospira concinna, Hall. Pal. N. Y., Vol. IV., p. 2791867. 



Shell small, depressed, sub-spheroidal, nearly circular in outline ; width 

 being usually a little greater than length ; valves sub-equal. Ventral valve 

 regularly convex, greatest convexity a little above middle, and curving regu- 

 larly to the sides and front ; umbo prominent ; beak neatly pointed and in- 

 curved over apex of dorsal valve, leaving a space between which sometimes 

 exposes the narrow area. There is usually a narrow depressed line from beak 

 to base of valve ; but this is often absent, or so faint as not to be readily ob- 

 served. Dorsal valve regularly convex, sometimes gibbous, becoming a little 



