I'M 2] The Ottawa Naturalist. 45 



merit of the interbrachials in that species render impossible any 

 confusion with the present form. 



Glyptocrinus circumcarinatus, sp. nov. 



Type specimen No. 668 T, University of Toronto Museum. 



Formation Trenton. 



Locality Kirkfield, Ont. 



Collector Joseph Townsend. 



A FOSSIL STARFISH WITH AMBULACRAL 

 COVERING PLATES. 



By George H. Hudson. 



(Continued from May number). 



The Covering Pieces or Epineurals. 



This specimen still retains 23 plates covering the food 

 grooves in such perfectly normal positions that there can be no 

 doubt whatever as to their being strictly homologous with the 

 epineurals of Edrioasteroidea. 



On the less developed portion of arm I (plate II, figs. 1,2, 

 3 and 6) there are 16 of these and on the mature portion of 

 arm IV, next the disc (plates I. figs. 1 and 3 ; III, figs. 3 and 4) 

 there are seven more. In addition there are 10 other epineurals 

 Avhich are but slightly displaced and whose proper position may 

 be easily recognized one on radius III, seven on radius IV 

 and two on radius V. Three other displaced and weathered 

 epineurals are also present. 



The most distal epineural on arm IV (the eighth of a series) 

 lies flat on the floor of the food groove and clearly reveals the 

 shape of the arm members of a series. They are pentagonal in 

 outline, twice as long as broad, the two long sides parallel; 

 the ends next the marginals have three angles each, the cen- 

 tral one of about 85 and well rounded at the apex; each free 

 end is truncate, having two right angles. 



Now when we have an ambulacral groove with straight 

 bordering walls we would expect the epineurals to be placed 

 alternately, their truncate ends against the wall and their pointed 

 ends toward the entrant angles between two neighbors of the 

 opposite row as in Cyathocystis. We also would expect these 

 inner ends to meet with their marginal faces apposed to each 

 other in close fitting valvate closure and the ridge formed by 

 the plates, when closed, to be low T and comparatively smooth 

 (plates flush), to secure additional strength against attack. 



