MISSISSIPPIAN LOOP-BEARING BRACHIOPODA 443 



the brachial valve, but the brachidium of Harttina is elongate, 

 like that of Cryptonella, reaching nearly to the front of the shell, 

 while that of Girtyella is short, like the brachidium of Dielasma. 

 Genotype. — G. indianensis (Girty). Other species, G. turgida 

 (Hall), G. brevilobata (Swall.). 



Dielasmotdes n. gen. 

 Description. — Shell terebratuliform. Pedicle valve bisinuate 

 toward the front in the genotype, the two depressions separated 

 by a low, broadly rounded mesial elevation; the foramen large, 

 oblique, encroaching wholly upon the umbonal region. Brachial 

 valve with a slight mesial flattening or depression anteriorly in the 

 genotype. Internally the dental lamellae are well developed in 

 the pedicle valve; in the brachial valve the socket-plates are sup- 

 ported at their inner margins by a pair of lamellae which pass 

 obliquely toward the floor of the valve to which they are joined 



Fig. 3. — A series of seven cross-sections (X2I) of the rostral portion of the shell 

 of Dielasmoides bisinuata n. sp., in the last three of which only the brachial valve is 

 shown. 



near the median line; between these lamellae, the outer walls of 

 the valve and the socket-plates, are a pair of cavities narrowly 

 triangular in cross-section which expand anteriorly and open out 

 into the general cavity of the valve; the crura originate from the 

 anterior extensions of the inner walls of the socket-plates. Form 

 of the brachidium not known. 



Remarks. — The characters of the rostral cavity of the brachial 

 valve in this genus differ from those of Dielasma in the absence 

 of any special crural lamellae distinct from the socket-plates. 

 The two rostral cavities, narrowly triangular in cross-section, have 

 a superficial resemblance in the two genera, but the narrow base 

 of the triangle in this genus is formed by the socket-plate, while 

 in Dielasma it is formed by the basal portion of the crural lamellae, 

 and the special muscle-bearing plate between the bases of the 

 crural lamellae of Dielasma is absent in this genus. This form is 



