MARYLAND GEOLOGICAL SURVEY 333 



small and situated on a line drawn across the glabella at the anterior 

 fourth; ocular ridge well denned, smooth, prolonged, with a backward 

 curve outside of the eye. Thorax a little more than half the width of the 

 head; the axis strongly convex and gradually tapering backwards; side 

 lobes flat; plurae with a wide groove along the middle, a small portion of 

 their outer extremities turned backward. Surface of thorax, glabella and 

 a subrenif orm space on each side of the base of the glabella smooth ; the 

 border with circular punctures about 0.2 mm. in width; the punctures 

 large and more distant at the inner edge of the border; on the elevated 

 part of the cheeks they have a subreticulated arrangement." Billings, 

 1865. 



This splendid species of which a nearly complete example has been 

 described as above by Billings, is represented in the Trenton fauna at the 

 base of the Martinsburg shale by fragments only, which, however, agree 

 fairly well with the corresponding parts" of the specimen figured by 

 Billings and here reproduced on pi. LI. 



Occurrence. MARTINSBURG SHALE (Sinuites bed). Chambersburg, 

 Pennsylvania. Trenton limestone of Ontario, New York and Minnesota. 



Collection. TJ. S. National Museum. 



Family TRINUCLEIDAE 



Genus GRYPTOLITHUS Green 



CRYPTOLITHUS BELLULUS (Ulrich) 



Plate LVI, Figs. 5, 6 



Trlnucleus bellulus Ulrich, 1878, Jour. Cincinnati Soc. Nat. Hist., vol. i, 

 p. 99, pi. iv, fig. 15. 



Description. " Body small, nearly flat, and symmetrical. Cephalic 

 shield about three times as wide as long, subquadrate, with a distinct 

 thoracic ring at the base, which is straight, with the posterior angles 

 acutely angular or slightly rounded, and without any long spines ; glabella 

 prominent, pyrif orm and produced posteriorly, into a long spine, reaching 

 to the pygidium ; cheeks not as prominent as the glabella, triangular, and 

 finely punctate; marginal fillet wide, marked in front by from three to 



