DIKELOCEPHALUS OF MINN B S 0 T A. 



575 



and protuberant; in the area, in front of the glabella, being much narrower and convex rather than con- 

 cave ; in the pygidium being only provided with a simple border, and in its axal lobe having but four 

 segments. 



Number of thoracic segments not known. Fig. 4, Tab. T. A, is in all probability, the wing-piece and 

 lateral spine of the cephalic shield of this species, as it is found at the same locality, associated in the 

 same layers with fig. 3, a and b, Tab. I. No caudal spines have been found attached to the pygidium of 

 this species, but it is not improbable that they existed. 



Dimensions. — Cephalic shield 1 inch long, 1 T 4 0 wide from eye to eye ; caudal shield j 8 jj inches long, 

 1j 4 q wide. 



This species is found in greatest abundance in soft gritstones of a light greenish-gray colour ; the third 

 Trilobite-bed of F. 1, two hundred to two hundred and twenty feet below the top of that formation, near 

 the mouth of the Miniskah River, at Mountain Island and elsewhere, associated with Orthis and Lingula. 



DIKELOCEPHALUS IOWENSIS. (N. S.) 

 (Tab. I., fig. 4, and Tab. I. a, fig. 13.) 



Specific character. — This species is merely known by its pygidium ; it is supposed to belong to the 

 genus Dikelocephalus, from the number of segments (4) of its axal lobe being the same as in the last 

 (fig. 3), but it differs from it in being of smaller size, and in being provided with flattened caudal spines, 

 set wide apart, larger in proportion than those of D. Minnesotensis, and, unlike them, they extend in curves 

 obliquely outwards ; border bounding the pygidium, simple and narrow. On the same slab with the 

 Trilobite, and beneath it on fig. 4, are the compressed subconical bodies, which, very probably, are the 

 detached caudal spines of larger individuals of the species. The individuals at present brought to light 

 are much smaller than either of the preceding. Number of thoracic segments not known. 



Dimensions. — Caudal shield A inches long, A wide. 



It occurs near the palosozoic base of the lowest sandstone of the Upper Mississippi, below Mountain 

 Island, and near the mouth of Black River, associated with Lingula and Obolus; more than five hundred 

 feet below the base of the Lower Magnesian Limestone, F. 2. 



DIKELOCEPHALUS GRANULOSUS. (N. S.) 

 (Tab. I., fig. 7 (and 5?).) 



Specific character. — This species is distinguished particularly by the glabella and cheek-plates, as far 

 as they are preserved, being studded with minute granules. The glabella is divided by three furrows 

 into four segments : the posterior segment terminates on either side in two obscure basal tubercles. 



Fig. 5 of Table I. is supposed to be the caudal shield of this species ; it is wider in proportion to its 

 length than any of the preceding species, and parabolic in form. Its axal lobe has three to four seg- 

 ments ; a narrow and thickened border. 



Dimeitsions. — Caudal shield, ^ inches long, one inch wide ; cephalic shield, ^ long, as far as pre- 

 served. 



This species occurs in the third Trilobite-bed, at the mouth of Miniskah River, associated with a small 

 Orthis, and another Trilobite, Tab. I., fig. 11, more than two hundred feet below the base of the Lower 

 Magnesian Limestone, F. 2. 



LONCHOCEPHALUS. (N. C). 



Generic character. — In this small and singular genus the highly-arched glabella is either undivided, 

 or has only two very obscure furrows. A spine of greater or less length projects backwards from the base 

 of the glabella, in the median line of the body over the thoracic segments; fig. 12, Tab. I. A. The 

 pygidium found associated in the same beds is semilunar, with little or no border, and has four segments 

 of the axal lobe. 



