442 



STUART WELLER 



Genotype. — D. elongata (Schl.). Other species, D. formosa 

 (Hall), D. shumardianum (Miller), D. fernglenensis Weller, D. 

 burlingtonensis White. 



Girtyella n. gen. 

 Description. — Shell terebratuliform. The pedicle valve sinuate, 

 with a large, subcircular or subovate, oblique foramen which 

 encroaches upon the umbo; the brachial valve frequently sinuate 

 and often with a slight median fold in the bottom of the sinus. 

 Internally the dental lamellae are well developed in the pedicle 

 valve. In the brachial valve the socket-plates are joined by a 

 concave hinge-plate which is imperforate at the apex and is sup- 

 ported by a median septum; the inner sides of the dental sockets 





Fig. 2. — A series of nine cross-sections (X2§) of the rostral portion of the shell 

 of Girtyella indianensis (Girty), three of which show both the pedicle and brachial 

 valves, the others showing only the structure of the brachial valve. 



retreat from the margins of the valve anteriorly beyond the point 

 of articulation, and become the bases of the crura which are still 

 joined by the concave hinge-plate and are also supported by 

 lamellae resting against the inner surface of the lateral slopes of 

 the valve. The brachidium short, its free portion apparently 

 being like that of Dielasma and not reaching to the middle of the 

 shell. 



Remarks. — Members of this genus have commonly been included 

 in the genus Dielasma, but they differ fundamentally from that 

 genus in the presence of a median septum supporting the hinge- 

 plate of the brachial valve, and in the origin of the bases of the 

 crura from the socket-plates. In his description of the species 

 which is selected as the genotype, Girty referred the form to the 

 genus Harttina on account of the presence of a median septum in 



