70 G. F. MATTHEW : ILLUSTEATIONS OF 



the following difFereuees : it is proportionately narrower, and tlie two small lobes at the 

 base of the glabella are larger ; the pygidia of the two species are quite different. This is 

 one of the most plentiful of the Agnosti of Div. i.c, and resembles the Scandinavian 

 species, A.fallax; from that species it differs in the form of the front lobe of the glabella, 

 and in having only three lobes in the posterior segment of the thorax. 



Length, 11 mm. Width, 5 mm. 



Horizon and Locality. Common in the shales of Div. I.c, at Portland, and at Hanford 

 Brook, St. Martin's. 



Agnostus vir, var. a. OONCINNUS, n. var. (Plate VII. Figs. 4«, b and r.) 



This form is very nearly related to A. vir, but presents the following differences : the 

 glabella is cylindrical, is proportionately longer, and the cross-furrow is directly trans- 

 verse ; the lateral lobes of the glabella are narrower. In the thorax the first segment 

 carries five lobes, the middle lobe being segmented. In the pygidium at the anterior end 

 of the rachis, a small triangular lobe is faintly defined on each side, and both the 

 marginal fold and furrow are more distinct than in the type. This variety is smaller than 

 the type. 



Length, about 9 mm. Width, 3| mm. Cephalic shield, 4 by 3| mm. 



Horizon and Locality. In the fine dark shales of Div. \.d, at Porter's Brook, St. Martin's. 

 Common. 



Agnostus Acadicus, Hartt. (Plate VII. Figs. 5a and h.) 



Acad. Geol. 2nd. Ed. pp. 655-6, Fig. 229. U. S. Geol., Surv., Bull. 10, p. 22. PI. II. 

 Figs. 2, 2a, b and c. 



The late Professor C. H. Hartt described two species of Agnosti from the St. John group, 

 that above-named and A. similix. Mr. C. D. "Walcott, however, who has studied the type 

 specimens of the Hartt collection now in Cornell University, finds that the latter species 

 is founded on a narrow straight-sided test of A. Acadicus ; and A. similis must, therefore, be 

 considered as a synonym of that species. For the purpose of comparison with other forms, 

 I give a figure of this species {A. Acadicus.) 



Horizon and Locality. This species is common in the shales of Div. l.r, but is not so 

 plentiful as A. vir- 



Agnostus Acadicus, var. ex. declivis, n. var. (Plate VII. Figs. 6a and b.) 



This form is closely allied to A. Acadicus, but presents the following differences : it 

 has a narrower border fold, and smaller basal lobe to the glabella ; the glabella has pro- 

 portionately a longer anterior lobe, and the furrow dividing it from the posterior lobe is 

 directly transverse ; the posterior lobe is strongly elevated, almost tumid behind, and bears 

 a small round tubercle at the middle of its length ; in front of the tubercle the lobe slopes 

 downward rapidly to the cross-furrow. 



Differences of equal import are found to exist between the pygidia of the two forms. 

 In var. declivis, the axial lobe is cylindro-conical, and there are three minute lobes on each 

 margin near the anterior end ; in A. Acadicus, the axial lobe has a more triangular form, and 

 both head and tail shields are found of a larger size than are those of the variety. 



