1909] The Ottawa Naturalist 155 



secondary ridges appear across the sutures between adjacent 

 radials and also between the radials and the first interbrachials. 

 The parts of the plates, not occupied by the radial carinae or the 

 above-mentioned ridges, are covered by a delicate granulation. 

 The prominence of these ornamental elevations and their unusu- 

 ally lineal character give the impression of a polygon surrounding 

 each radial, with its angles connected to the centre of that plate 

 like the spokes of a wheel. Less pronounced ploygons also appear 

 around each plate of the third circlet, but higher up the cup, 

 this impression is lost on account of the increasing irregularity 

 of the plates and the more pronounced petaloid character of the 

 ridges. 



The beauty of the organism is further increased bv the 

 peculiar manner of origin of the first and second pinnulas. The 

 radial plates bifurcate on the second primibrach (prim axil, 

 second costal) and a row of non-stellate but granulated plates 

 lies between the two divisions of the ray. The prominent carinae 

 are continued up the secundibrachs (distichals) into the arms. 

 From each of the second secundibrach, lateral branches of the 

 carinae pass outwards and upwards into the notch between the 

 arms of contiguous rays. Wachsmuth and Springer interpret 

 these lateral extensions of the carinse as pinnulae: they appear 

 however to be an integral part of the plates over which they pass 

 and may be considered as the carinae of tertibrachs (palmars), the 

 continuation of which into arms has not been completed. This 

 explanation seems reasonable in view of the fact that twenty 

 is the normal number of arms in the Glyptocrinidcs. Following 

 Wachsmuth and Springer, however, the third secundibrach 

 (distichal) is without a plume but from the fourth, a strong 

 pinnule passes inwards and upwards to becom.e confluent with 

 its mate in the depression between the two arms of the same 

 rav. It is this peculiar arrangement of the lower pinnulo- which 

 induces me to believe that my specimens belong to Billings' 

 species. Were it not for this agreement in a unique feature, the 

 difference in ornamentation and in the general shape of the cup 

 might be considered sufficient ground for the establishment of a 

 new species. 



Periglyptocrinus priscus, as emended above, is a fairly large 

 and unmistakable species and is the mo.st beautiful form among 

 the many Crinoids from the Trenton Formation in Ontario. 



Horizon Trenton. ^^ 



Location Balsam Lake, Ontario. 



Collector Mr. Joseph Townsend. 



Specimen Number 649 T. University of Toronto Museum. 



