382 New Species of Trilobites* 



with the longitudinal axis of the body. The direction of the 

 next pair is the same only that the curve is nearer the axis. The 

 other three pairs are nearly parallel throughout. 



The length of the axis of the pygidium is a little greater than 

 the length of the central or terminal pair of ribs, and its last seg- 

 ment is triangular. The ribs are all pointed at their extrem- 

 ities and appear to project a little beyond the true margin of the 

 pygidium. 



In addition to the small specimens above figured, we have sev- 

 eral other imperfect tails about three-fourths of an inch in length 

 each. In these the ribs are more cylindrical and distinctly sepa- 

 rated, and more curved outwards than they are in the small spec- 

 imens. The axis is convex and obtusely angular along the middle. 

 These differences I think may be the changes induced by the 

 growth of the individuals. The species probably attained the 

 length of one or two inches. 



Differs from the Russian species A. Fischeri (Eichwald) in 

 having the extremities of the ribs of the pygidium pointed instead 

 of obtuse, and from A. Lindaueri (Barrande) in having them 

 more nearly.parallel. 



It is an interesting fact that associated with this trilobite, the 

 only species of the genus yet found in the Canadas, we find a 

 group of Cystidew, allied to the European Echinosphcerites, and 

 also a Bolboporite closely allied to the B. mitralis, which occurs 

 along with A. Fischeri in the Lower Silurian rocks of Russia. 

 Our coral has a smooth hemispherical solid base, and a small con- 

 ical celluliferous upper extremity, often slender and pointed and 

 half the whole length. It appears to me to be a distinct species, 

 and it might be called B. Americana. 



Locality and formation. — A. Canadensis ocurs in the Chazy 

 Limestone at the Mingan Islands, and also in the same formation 

 near Montreal. In both localities it is associated with B. Amer- 

 icana. 



Collector. — Sir W. E. Logan. 



Triarthrus glaber. (n.s.) 



Description. — This species closely resembles T. Bec7cii, but has 

 not the row of short spines along the middle of the axis. In 

 specimens that are crushed quite flat, the form is elongate oval, 

 and obtuse at both ends. The length is about twice the width, 

 the central lobe as wide as the side lobes, or very nearly so. In 



