280 bulletin: museum of comparative zoology. 



far at the sides as those behind — a common condition in trilobites with genal 

 spines. 



The pygidimn is nearly semicircular, but has the somewhat triangular 

 appearance so often seen in pygidia of ampycids or trinucleids. The axial 

 lobe is narrow, elevated, and extends almost to the posterior border. The 

 pleural lobes are flat, and turn down but little to the very narrow thickened 

 margin. Singularly enough, there is a ring on the axial lobe for each pair 

 of ribs on the pleural lobes, so that rings and ribs are continuous. Nine dis- 

 tinct rings are present. The ribs are narrow and flat, with just a suggestion 

 of an impressed line along the top. 



Measurements: — Length 14.5 mm., greatest width, 13 mm., width at 

 middle of thorax, 10.5 mm. Length of cephalon 6.5 mm., width 13 mm.; 

 length glabella 4.5 mm., width of glabella at front 3.25 mm. Length of thorax 

 4 mm., width 10.5 mm.; width of axial lobe 2 mm. Length of pygidium 

 3.25 mm., width at front 9 mm.; width of a.xial lobe at front 1.5 mm. A flat- 

 tened cephalon is 6 mm. long, 15 mm. wide, and the glabella is 4.5 mm. long. 



This species differs in many respects from Endymionia meeki. The 

 glabella is shorter and considerably narrower, has four instead of two 

 pairs of pits at the sides, and has much less prominent lobes beside it. 

 E. meeki does not seem to have the mound-like cheeks, and eye-lines 

 are absent. The axial lobe of the thorax is much narrower in A. 

 glacialis than in E. meeki, and the furrows on the pleura are straight 

 instead of sinuous. The pygidium of the present species has a nar- 

 rower axial lobe and more rings and ribs than in the Beekmantown 

 form. 



With the knowledge of this specimen it is possible to get a better 

 idea of the characteristics of the Endymionidae. The form of the 

 thorax and pygidium and the presence of narrow free cheeks approach 

 very closely to the Raphiophoridae, being excluded from that family 

 as now defined only by the shortness of the glabella and the absence 

 of a long spine therefrom. 



Horizon and Locality: — Billings's specimens came from the 

 conglomerates of Portland Creek and Pistolet Bay, Newfoundland. 

 Hyatt found it on the east side at Port au Port, and Schuchert and 

 Twenhofel obtained three fragments from the same locality. The 

 horizon is their zone 6, Normanskill. Genoholotype M. C. Z. 1,594. 



Olenidae Burmeister. 

 Triarthrus caecigenus, sp. nov. 



Entire test oval, of the usual shape in this genus, without spines or pustules 

 except for a small one on the neck-ring. 



