SILURIAN AGE. 9 



sequently proposed genera. The other names applied by Corda fall into the list of 

 synonyms, just as if they had been proposed by any other author at any subsequent 

 time. 



Agraulos Oweni. 



Arionellus {Crepicephalus) Oweni, Meek & Hayden, Proceed. Acad. Nat. Sci. Phila., December, 1861, p. 436. 

 Arionellus? Oweni, Meek & Hayden, Am. Jour. Sci. Sec. Ser. XXXIII, 74, January, 1862. 



Head semi-circular, or nearly semielliptic in outline, its length equalling about two-thirds its breadth, rather dis- 

 tinctly convex ; posterior margin more or less concave in outline, and provided with a deep, rounded marginal 

 groove along each lateral slope. Glabella oblong-subovate, rather gibbous, elevated above the cheeks and tapering 

 towards the rounded front with slightly convex lateral margins ; greatest convexity near the middle and behind ; 

 separated from the cheeks, on each side and in front, by a distinct furrow ; neck furrow passing entirely across, but 

 slightly deeper on each side than at the middle ; lateral grooves three, very short, obscure, or (in casts) nearly obsolete, 

 and but slightly oblique. Cervical segment a little convex at its posterior outline, less elevated than the glabella. 

 Anterior slope in advance of the glabella less than half as wide as the length of the latter, and provided with a 

 distinct, rounded transverse furrow, which passes around slightly in front of the middle of the space parallel to 

 the anterior and antero-lateral margins. Cheeks convex, and sloping towards the lateral and antero-lateral bor- 

 ders. (Surface and facial sutures unknown.) 



Length of cephalic shield, measuring from the posterior side of the neck segment to the front margin, 0.57 inch ; 

 greatest breadth, measuring across at the posterior extremities of the cheeks, 0.87 inch ; height, 0.31 inch. Length 

 of glabella, including the neck segment, 0.40 inch ; breadth of glabella, 0.35 inch. 



Head of a young 

 Profile view of head. \=^^r=rr^S? individual. 



Agraulos Oweni. 



A. Side view of a cephalic shield of Agraulos Otoeni, the position of the eyes (which have not been distinctly seen) 



indicated by a dotted line. 



B. Another view of the same, and of a small pygidium supposed to belong to the same species, with the body restored 



in outline. In this cut the marginal furrow passing around the front of the head is made to terminate rather 

 too abruptly on each side ; while the lateral furrows of the glabella are indicated too distinctly. In the 

 specimens these furrows are very obscure, and it is difficult to see whether there were only two, or more on 

 each side. 



C. Head of a young individual, same species. 



The only specimens of this species yet obtained are casts, which show no traces 

 of the sutures, and retain no remans of surface granulations, strise, or other mark- 

 ings, if there ever were any. Nor are they in a condition to show whether or not 

 the postero-lateral extremities of the buckler are pointed, though they probably are. 

 At a point nearly opposite the middle of the glabella, there is on each cheek, less 

 than half way down the slope from the furrow between the fixed cheeks and the 

 glabella, the remains of a small eye, though the specimen being unfortunately a 

 little defective here on both sides, the exact form of these prominences cannot 

 be clearly made out. 



In the same slab containing the cephalic shield above described, we observe a 

 pygidium which probably belongs to the same species. It is sub-semicircular in 

 form, moderately convex, and rather distinctly, as well as nearly equally trilobate. 



2 February, 1864. 



