[MATTHEW] STUDIES ON CAMBRIAN FAUNAS 49 



DOLICHOMETOPUS, Angelin. 



DOLICHOMETOPUS OCCIDENTALIS, n. Sp. (PI. 11., fig. 2.) 



Body ovate, with short genal spines and broad prominent rachis. 



Head-shield narrowly semi-circular. The glabella cylindrical, some- 

 what narrow in the middle, about half longer than wide. Two furrows 

 are visible at the side of the glabella, the posterior directed backward 

 In this example the front of the glabella is not well preserved. The 

 occipital ring is divided from the glabella by a distinct furrow and bears 

 at the back a low spine or tubercle. The fixed cheek within the eye-lobe is 

 about a third as wide as the glabella, but at the back is more than half 

 as wide. The eye-lobe is long, narrow, and but slightly arched, its length 

 is about two-thirds of the width of the glabella. The dorsal suture 

 arches outward in front of the eye, and also more decidedly so behind the 

 eye, the proportion of the three cords counting from the front is about 

 3|-, 6, 4. The posterior marginal fold is broad and the furrow wide. 



The movable cheek is short and wide, and has a wide border; the 

 area of the cheek at the front of the eye is as wide as the marginal fold, 

 at the back it is a half wider ; the cheek ends in a short obtuse spine. 



The thorax is composed of eight segments, and is about one-third 

 wider than long. The rachis is wide, wider in front than the back part 

 of the glabella. The rachis is, one-quarter wider in front, than the 

 length of the pleura, but at the back of about the same width, the ring is 

 prominent, has a deep furrow in front and bears a tubercle or spine at 

 the back. The pleura has a deep triangular furrow running along the 

 middle nearly to the end ; it is broad at the rachis, next which there 

 is a small elevation in the middle of the furrow, and becomes narrow and 

 fiides out toward the end of the pleura, the end of which is flattened, 

 rounded, and apparently devoid of a spine. 



The pygidium is semicircular, and about twice as wide as long 

 The rachis is large and prominent, has three somites and extends nearly 

 to the extremity of the pygidium. The side lobes are marked by two 

 deep grooves, which alternate with two other grooves that are deepened 

 toward the margin ; the posterior grooves have the extremities curved 

 backward ; the posterior margin is flattened and the fold is weak. 



Sculpture. — The outer surface is unknown, and the inner surface, 

 minutely punctate. 



Size. — Only one example is known. This is 12 mm. long and 8 mm. 

 wide at the genal spines. The head-shield is 5 mm. long. The thorax is 

 5 mm. long and 7 mm. wide. The iD3'gidium is 2 mm. long and 4 wide. 



The discovery of this species enables us to fill out more completely 

 the diagnosis of this genus. Apparently only the middle piece of the 

 head-piece has been known in Sweden. The author's study of Hastings 



Sec. IV., 1899. 4, 



