CONTRIBUTIONS TO PALEONTOLOGY. 107 



PROETUS MACROCEPHALUS, var. a, 

 A specimen uearly entire, and several pygidia, present some variation 

 from the strict characters given of the preceding. The pygidia are semi- 

 circular, twice as wide as long ; the rings of the axis distinctly nodose on 

 the summit, and the little pustulose maikings of the ribs on the lateral 

 lobes are arranged in two rows. 



There are four specimens exhibiting the form of pygidium and character 

 of surface indicated ; and another, with a semicircular pygidium, has the 

 ribs angular. 



Geological formation and locality. In the shales of the Hamilton group: 

 at Moscow and Bloomfield ; and in a stratum of limestone in the Hamilton 

 group, at Eighteen-mile creek on Lake Erie. 



PROETUS AURICULATUS (n.s.). 

 Glabella round-ovate, the length equal to the greatest breadth 

 across the posterior lobes : anterior to the furrows, the breadth 

 is one-fifth less; the measurements being five-eighths, and half 

 an inch. The anterior and middle furrows are gently curved; the 

 posterior one more oblique, and deeply separating the short ovoid 

 posterior lobe from the body of the glabella. The occipital furrow 

 is strongly defined ; the border is deeply depressed immediately 

 in front of the glabella, rising abruptly beyond, and again de- 

 pressed in a narrow groove, with the margin recurved. 

 In the same association there has been found a pygidium with a 

 very prominent rounded axis, terminating abruptly behind, and 

 marked by nine or ten direct rings; and the lateral lobes by seven 

 or eight ribs ( the posterior ones being obscure, as are the rings of 

 the axis), terminating in a wide spreading border. The glabella is 

 distinguished by its very convex form, the equal length and breadth, 

 and the distinct separation of the posterior lobes. The axis of the 

 pygidium is proportionally broader and stronger than in any other 

 species described in this paper. 



This species very nearly resembles the Proetus missouriensis of Shumard 

 ( Geological Report of Missouri, pa. 196, pi. B, f. 13 a, J ) ; but the gla- 

 bella is proportionally longer. There is a less degree of similarity in the 

 pygidim of that species, and the one found associated with the glabella of 

 this species. 



Geological formation and locality. In shaly sandstones of the age of the 

 Chemung group : in Licking county, Ohio. 



1861.] 



