38 bulletin: museum of comparative zoology. 



from the "Niagara" at Cicero, Illinois (M. C. Z. 629). A second 

 specimen, tentatively referred to this species, is in the Museum of the 

 Geological Survey of Canada, and is from the Guelph of Hespeler, 

 Ontario. 



Cheirurus tarquinius Billings. 



Cheirurus tarquinius Billings, Proc. Portland soc. nat. hist., 1863, 1, p. 121, 

 pi. 3, f. 22. 



This is a little-known species of the Ch. insignis group. It has a 

 short, wide cephalon, narrow triangular basal lobes on the glabella, a 

 short frontal lobe, and the first two pairs of furrows turn backward, 

 are quite straight, and are intermediate in length between those of 

 Ch. niagarensis and Ck. welleri. The species is especially characterized 

 by the forward position of the eyes, which are opposite the second 

 glabellar lobes, and the consequent small free cheeks and long fixed 

 cheeks. The genal angles appear to be spineless. 



The type is No. 3081 in the Museum of the Geological Survey of 

 Canada. Associated with it is a pygidium from the same locality. 

 It is of the insignis type, with three pairs of spines, but the median 

 spine is shorter and more rounded than in either Ch. insignis or Ch. 

 niagarensis. A poorly preserved hypostoma in the same collection 

 has the posterior end more rounded than that of Ch. niagarensis, and 

 thus more like that of Ch. welleri. 



Measurements: — The type (G. S. C. 3081) is 19 mm. long, 35 mm. 

 wide; and the glabella is 12 mm. wide at the neck-ring and 17 mm. 

 wide at the frontal lobe. 



Formation and locality: — Middle Silurian at Port Daniel, Bay, 

 Chaleur, P. Q., Canada. Also reported by Billings from Masardis, 

 Maine. 



Cheirurus hydei (Weller). 



Ceraurus hydei Weller, Bull. Chicago acad. sci., 1907, no. 4, pt. 2, p. 264, pi. 24, 

 f. 22. 



This species is of more than ordinary interest, from its resemblance 

 to a Ceraurus. The cephalon and thorax are those of a typical 

 Cheirurus, but the pygidium is that of Ceraurus. This at once raises 

 the question as to whether this is a Cheirurus which has developed a 

 Ceraurus-like pygidium, or whether it is a Ceraurus whose cephalon 

 and thorax have developed in a manner paralleling that of Cheirurus. 



