62 CANADIAN FOSSILS. 



diameter, which is near the base of the free rays. The basal plates 

 are pentagonal, with an obscurely-rounded ridge across their base ; 

 sub-radials, hexagonal, each supporting upon its truncated upper 

 margin a large inter-radial. The first primary radial on each side of 

 the azygos inter-radial space is hexagonal, the other three are penta- 

 gonal ; the second plates in the rays are hexagonal, and the third 

 heptagonal ; each of the latter supporting upon its upper sloping 

 edges the bases of two secondary rays, which become free at the 

 third or fourth plate, thus furnishing ten arms, which divide at not 

 quite one-fourth of an inch from their base, and again at half an inch ; 

 the full grown arms are again subdivided, some of them once, others 

 twice. The arms are comparatively short, not exceeding two inches 

 in length in a specimen whose cup measures one inch and a half in 

 length. The ossicula which constitute the double series of joints of 

 the free rays or arms, are obtusely cuneiform, the two rows inter- 

 locking with each other so slightly that the points of the joints 

 extend but a short distance across the centre of the back of the 

 arm ; there are two ossicula to one line in length in that portion of 

 the arm at the base which is situated next the cup, and below the 

 first sub-division ; the arm here is scarcely one line in thickness. 

 All the plates are smooth or slightly granulated on their surface ; in 

 some of the specimens there is a trace of an obscurely-elevated 

 margin round the plates, and there is also a broadly-rounded keel, 

 not very prominent, upon each of the primary and secondary rays. 

 The column is round, slender, annulated, with thin but round- 

 edged projecting joints, for several inches below the bottom of the 

 cup ; it then becomes smooth, and continues of an uniform size to 

 the base of attachment, which consists of a number of root-like 

 branches. The annulated portion of the column is usually found a 

 little curved, but the smooth, cylindrical portion is always straight, 

 and in this part there are about ten joints to two lines of the length ; 

 near the cup there are three or four annulations to two lines. The 

 diameter of the column is from one and a half to two lines and 

 a half, and the length varies greatly ; one specimen, a very perfect 

 impression of the head, column and root, all in their natural connec- 

 tion, measured but seventeen inches in length ; a fragment of the 

 smooth portion of a column still lying in the rock measures thirty- 

 seven inches and a half. At Ottawa, in the upper part of the 

 Trenton limestone, there are fragments of smooth, round columns, 

 four or five lines in diameter, which appear to be a large variety of 

 this species. 



