24 [Assembly 



Genus Nucleospira (Hall, 1857). 



Spirifer .• Muechison, Sowerby, et al.; Orthis .• Hall. 

 [ Gr. TtVQ-qv, nucleus; GTtEiga, spira.} 



Shell spheroidal or transversely elliptical, more or less gibbous or 

 ventricose, furnished with internal spires as in Spirifer : hinge- 

 line shorter than the width of tlie shell ; cardinal extremities 

 rounded : valves subequal, articulating by teeth and sockets. 

 Ventral valve having the beak extended beyond the opposite 

 valve, and beneath it a triangular depression or area, which 

 sometimes terminates in a shallow spoonshaped pit; on each side 

 of which, at the base, is a strong tooth. A narrow ridge or septum 

 extends along the centre of the inner side of the valve, from beak 

 to base. Dorsal valve furnished with a strong spatulate cardinal 

 process, which, rising vertically from the cardinal margin, is 

 closely grasped at its base by the cardinal teeth of the other 

 valve; and thence bending abruptly upwards, and expanding, is 

 projected into the cavity of the opposite beak, lying close upon 

 the underside of the false area. This process is grooved or de- 

 pressed in the centre 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 the protrusion of which a minute foramen is 

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

 above the junction of the teeth of the opposite valve, and at the 

 point where it bends upwards, originate the crural processes 

 which support the spires. A deep cavity beneath the cardinal 

 process extends to the dorsal beak, from which originates a thin 

 elevated septum running to the base of the shell. Muscular im- 

 prints confined to a narrow oval space. 



Surface apparently smooth; under a lens, punctate : shell structure 

 punctate, and, when perfect, covered with minute hair-like spines. 



The larger species of this genus present some analogy in external ap- 

 pearance with Spirigera, and the presence of internal spires increases the 

 Bimilarity. The cardinal teeth resemble those of Spirigera and Merista : 

 the punctate shell and the structure of the hinge are, however, quite dif- 

 ferent. In foimi, and in the punctate character, it simulates Ma^as; while 

 the elongate cardinal process of the dorsal valve resembles that organ in 

 Thecidium. The genus, however, when regarded in all its features, is 

 very distinct from any of these ; and tlae species will constitute, so far as 

 regards American palaeozoic bracliiopoda at present known, a well-marked, 

 beautiful, and interesting little group. The geological range of the genus, as 



