100 CONTRIBUTIONS TO CANADIAN PALEONTOLOGY. 



subovoid and truncated above, or obscurely nine-sided with the up25er 

 side much the broadest, resting against the sides of the second and 

 third primary radials, and about equal in height to both of the latter. 

 Second interradials much smaller than the first, about twice as broad 

 as high, hexagonal (or possibly quadi'angular) in outline. Above each 

 of the second interi-adials there are three plates, the central one jjen- 

 tagonal and broader than high, with a minute and apparently hexa- 

 gonal plate, which is higher than broad, on each side of it. These three 

 plates are in each case placed between the arm bases of two contig- 

 uous rays. 



Dome plates polygonal, varying in shape and size according to their 

 relative position, s<jme of those in the interradial areas being slightly 

 larger than any of those in the radial. Anal ajjertiire nearly but not 

 quite central. 



The sculpture of the outer surface of the plates of the dorsal cup con- 

 sists of numerous raised ridges which radiate from a large and promi- 

 nent tubercle in the centre of each plate. In the radial series the first, 

 second and third primary radials ai-e connected by a continuous ridge, 

 which is broader and more prominent than any of the other radiating 

 ridges in these plates, and this bifurcates, ia the centre of each third 

 primary I'adial, into two branches which diverge outwards and upwards 

 through the secondary radials as far as the commencement of the arm 

 bases below. In the interradial series, a ridge which is also broader 

 and more prominent than the other radiating ridges, commences in the 

 middle of the lower margin of each of the first primary interradials and 

 extends upwards as far as the central tubercle. From this point it 

 bifurcates widely outward and upward until the extremity of each of 

 its branches reaches nearly as far as and almost coalesces with that of 

 the corresponding branch in the nearest secondary radial. 



The outer surface of the dome plates is very minutely granulose and 

 ornamented, with but few excejitions, by minute, low, isolated and 

 rounded tubercles, of which there are fi'om one to six in each plate. 



iSIaximum height of the only specimen known, about thirteen and a 

 half millimetres ; greatest breadth of the same, nineteen mm. and a 

 half. 



Kear Thedford, Rev. J. M. Good willie, 1882 : a single specimen. 



This species appears to be most nearly related to Bolatocrimis 

 triuilactylm of Barris, from the Hamilton Formation of Alpena, ^lich- 

 igan.='- 3Ir. Wachsmuth, who has kindly compared the type of D. 

 Canadensis, with authentic examples of D. triadactylus, in a letter to the 



• Licscribcd and figured in ithe " Pror-uedinsr- of the Davenport Academy nf Natural 

 Science.? " for 18S3. 



