Shinier — Specimen of Strenuella strenua (Billings). 199 



Abt. XIX. — An Almost Complete Specimen of Strenuella 

 strenua (Billings) ; by H. W. Shimek. 



The specimen of Streniiella strenua, here described, was 

 found at Mill Cove, North Weymouth, Mass., in the Lower 

 Cambrian slates. It is now in the collection of the Boston 

 Society of Natural History, with catalog number 12978. 



The cephalon is almost complete. The genal angles are 

 prominent ; the free cheeks thin, and the anterior fold (frontal 

 rim), extending around the front of the cephalon between the 

 free cheeks, is narrow, convex, and defined from the rest of 

 the cephalon by a prominent, rounded furrow. The glabella 

 is strongly arched, with two partial but well-marked furrows ; 

 it tapers forward very slightly and is abruptly rounded in 

 front. The neck ring is prominent, with anterior furrow 

 broad and deep, and the posterior shallow and narrow ; this 

 narrow furrow separates the neck ring from a strong, back- 

 ward-pointing, triangular projection, which shows no evidence 

 of a spine. The palpebral lobes are slightly curved and sepa- 

 rated from the fixed cheeks by a rounded furrow which disap- 

 pears anteriorly. What, with doubt, was taken for an eye, is 

 a small, lozenge-shaped elevation bordering the free cheek but 

 apparently attached to the palpebral lobe ; this was seen only 

 upon the left side. The fixed cheeks are convex but much 

 less so than the glabella ; they are not flattened on top. 



The axis of the thorax is quite convex, as are also the pleura. 

 The latter rise gently from the axis for slightly more than half 

 their length, when they bend clown quite suddenly, thus giv- 

 ing to them a triangular convexity. This down-bending takes 

 place just inside the point where the overlapping of the pleura 

 cease. There is a broad rounded furrow running lengthwise 

 through the middle of each pleural segment and terminating 

 in the straight, outwardly-pointed, broadly spine-like tip. The 

 anterior half of each segment as divided by this median fur- 

 row is narrower than the posterior. Nine segments are pre- 

 served on the specimen and judging from the shortening and 

 narrowing of the pleural portions of the segments, there were 

 very few if any more before the pygidium. 



The peculiar pleural segments of this specimen naturally 

 led at first to a comparison with Ellipsocephalus. The close 

 similarity of these segments with those of E. hoffi Schlotheim, 

 figured in Zittel's Textbook of Paleontology, is very evident ; 

 especially comparable is the broad groove in the middle of 

 each outwardly-pointing segment. But this specimen differs 

 from Ellipsocephalus in lacking the smooth glabella with its 



