APPENDIX. 



ARTICLE I. 



DESCRIPTION OP NEW AND IMPERFECTLY KNOWN GENERA AND SPECIES OF ORGANIC REMAINS, 

 COLLECTED DURING THE GEOLOGICAL SURVEYS OF WISCONSIN, IOWA, AND MINNESOTA, BY 

 D. D. OWEN. 



CRUSTACEA (TRILOBITES). 



DIKELOCEPHALUS. (N. G-.) 



Generic character. — Cephalic shield semicircular, and rather flat, glabella moderately convex, equally 

 wide throughout, rounded in front, divided by two furrows into three distinct lobes ; these well-marked 

 furrows extend quite across the glabella, and form a curve or slightly obtuse angle in the median line 

 directed backwards ; the anterior lobe is partially divided by a third obscure furrow, which becomes obso- 

 lete in the median line. 



Facial sutures distinct, originating at the anterior border of the cephalic shield ; they run at first 

 parallel with the same, then converging in a sigmoid flexure around the eye-plate, diverge again in curved 

 lines, until reaching the anterior border, they circumscribe an area of greater or less extent in front of 

 the glabella. 



The cheek-plates produced at their anterior corners into spines of moderate length, as indicated by 

 various detached check-plates, one of which, found in the buff-bed near the base of La Grange Mountain, 

 is shown by Fig. 3, Tab. L, A. 



Pygidium rather deeper and about the same width as the cephalic shield ; axal lobe smaller than the 

 lateral, with from four to six segments ; the last and largest segment sometimes obscurely subdivided by 

 a faint furrow. Lateral and interlateral segments blended into a marginal flap or border of greater or 

 less extent; usually, if not always, provided with caudal spines. 



Relations and differences. — The genus D ikeloceplialus approaches on the whole nearest to Ogygia, but 

 the middle lobe of the pygidium has fewer segments, and is much shorter and blunter ; the glabella is 

 not contracted posteriorly, and two transverse furrows extend quite across the glabella, in this respect 

 having a greater similarity to Trihhites Sternbergii,* but from which it also differs in the anterior 

 furrow, and in the basal lobe not assuming a tuberculated character. 



* See Table III., figs. 7 and 8, organization der Trilobiten, von Hermann Burmeister, for which Dr. Beyrich pro- 

 posed the generic name of Chirurus. This genus, as given by Hawle and Corda, differs, however, in the form and 

 lobes of the glabella from Burmeister's figure of this Trilobitc, and in the caudal shield there is a wide difference. 

 See Tab. VI., fig. 70, of their work. 



