92 



CRUSTACEA. * 



Genus Shifmakdia. (N. gen.) 



Generic Characters. — Head semicircular, with a convex, sub-cylindrical 

 glabella ; no eyes visible in the only species known. Pygidium about as 

 large as the head, with a prominent cyhndro-conical axis ; side lobes and 

 axis more or less distinctly ribbed. Thorax unknown. 



The only species of this genus known to me is a minute trilobite, evi- 

 dently allied to the genus Agnostus, from which it differs in having the 

 pygidium regularly ribbed like an Asaphus or Galymene. 



This genus is dedicated to the eminent American palaeontologist and 

 geologist, Dr. B. F. Shumard. 



Shumardia granulosa. (N. sp.) 



Fig. 83. 



Fig. %'i.— Shumardia granulosa, enlarged four diametera. a, the head ; 6, the 

 pygidium. 



Description. — Minute, ovate. Head nearly semicircular, length a 

 little more than half the width, strongly convex. Glabella irregularly 

 aub-cylindrical, broadly rounded in front, three-fourths the whole length 

 of the head, with a large tubercle on each side at the anterior extremity, 

 and a very minute one on each side next to the neck furrow, the latter 

 extending all across. Dorsal furrows on each side of the glabella very 

 deep, and angular at the bottom as far as the large anterior tubercles ; 

 around these and the front of the glabella, not so deep, yet still distinctly 

 defined. From the middle of the front of the glabella, a well defined 

 angular furrow runs straight forward to the middle of the anterior margin 

 of the head. In the bottom of this furrow there appears to be a small 

 triangular tubercle, which gives to the glabella, m some specimens, but 

 not in all, the appearance of having a projectuig angular point in the 

 middle of its front margin. The two large tubercles mentioned seem to 

 be simply a lateral expansion of the anterior one-fourth of the glabella, 

 making its width at this place one-third greater than it is at the mid-length. 



