[MATTHEW] STUDIES ON CAMBRIAN FAUNAS 57 



spine ; that the lateral lobes have five anchylosed segments ; that the 

 narrow margin bears six pairs of slender spines, one for each somite. 



It should be mentioned that the broad flattened ribs of the lateral 

 lobes of the pygidium have a depression in the middle of their somewhat 

 widened extremity. 



The movable cheek has not been described. The dorsal suture cuts 

 the anterior margin obliquely and curves in to the eye-lobe, which is 

 short and has little prominence ; behind the eye-lobe the suture turns 

 outward nearly to the genal angle, from the back of the eye to the front 

 of the shield the general coui-se of the suture is nearly parallel to the side 

 of the glabella. The proportion of the parts of the suture from the front 

 are 1|, I, 2. In fjont of the eye the area of the movable cheek is about 

 one and a half times as wide as the marginal fold, behind the eye it is 

 more than twice as wide. The cheek bore a spine, but as this is broken 

 the length is not known ; as the first three pleurœ apparently had no 

 spine, the genal spine probably extended as far back as the third pleural 

 segment. 



Sculpture. — The surface is granulated with elevations of irregular 

 form, which on the cheeks and glabella show a tendency to coalesce, 

 forming irregular rugulose ridges ; on the front of the glabella they have 

 an obscurel}'^ concentric arrangement. 



Size. — Length of head-shield, 20 mm. ; width, 34 mm. Length of 

 thorax, 15 mm., width exclusive of spines, 29 mm. Length of pygidium, 

 exclusive of spines, 15 mm. width, without the spines, 27 mm. Total 

 length, 50 mm. Loose pygidia show that these dimensions do not give 

 quite the full size 



A comparison of the head of this species, with that of Dorypyge 

 quadriceps.^ will show that it has all the generic characters of Dorypyge J 

 it differs from that species in its less massive occipital ring and posterior 

 border, and its more oblique ocular fillet. 



Zacanthoides spinosus, Walcott. 



Oxygia (?) spinosa, Wale, U. S. G. S. Monog. viii., p. 63, pi. ix., fig. 22. 



Olnoides spinosus, Wale, Bull. 30, p. 184, pi. xxv., fig. 6. 



Zacanthoides spinosus. Wale, Olenellus Zone, p. 586. 



Emholimlus spinosa, Roem., Acad. Nat. Sci., Phil., Proc, 1887, p. 15, pi. i., fig. 3. 



The occipital ring is said by Prof. Roeminger to have a triangular 

 projection, this is sometimes seen to project backwards in a spine that 

 may be 8 mm. long ; the base of this projection is bounded on each side 

 by a shallow furrow that crosses the occij^ital ring, dividing it into three 

 lobes. The ring has also a tubercle on this triangular projection, the 

 occipital spine is not connected with this, but with the back of the 

 triangular projection. 



' U. S. Geol. Surv. Bull. 30, PI., xxix., fig. 1 and la. 



