46 The Ottawa Naturalist. [June-July 



Our specimen violates every one of these conditions. The 

 epineurals are opposite; their pointed ends against the straight 

 border of the food groove; their thick, blunted, truncate ends 

 apposed to those of their neighbors of the opposite row; their 

 great length allows these ends to touch only by the inner edges 

 of their end faces (closure not valvate) ; when closed the ridge 

 is high, the angle at the summit being about 65 (plate II, figs. 

 3 and 6) ; the closure at the ends is often very imperfect (see 

 13th epineural in upper row, plate II, figs. 1 and 2 and the 5th 

 epineural in lower row on arm IV, plate III, fig. 4); the plates 

 are too wide to secure valvate closure at their lateral margins 

 and the majority have these margins imbricated and with either 

 the orad or aborad margins under. These plates, in shape and 

 arrangement, are so at variance with what we would naturally 

 expect that they call to mind the double row of flat spines that 

 protect the food grooves in Pentaceros. To derive the latter 

 from the former would seem to require less alteration that that 

 which has already taken place. 



Some of these changes might be considered as indicative 

 of a loss of the primary function, but the specialized form of 

 joint and free end and the marked increase in length, breath, 

 and thickness must be taken to indicate that these changes are 

 all adaptations secured by a new function or functions that were 

 added to the primitive one and finally came to surpass it in 

 importance. 



Two possible new functions will be considered; the first 

 of these a new method of securing food supply and the second 

 a new aid to locomotion. Before taking up either it will be 

 necessary to make a brief study of the evidences of the muscular 

 system which our specimen possessed. 



Musculation. 



That the epineurals are arranged alternately with the 

 adambulacrals below them may be seen by an examination of 

 the fourth and sixth epineurals of the lower row in plate III. 

 fig. 4. The position of the eleventh epineural of the upper row 

 in plate II, fig. 1, and the position which the tenth of this series 

 must have occupied will give additional evidence. In the last 

 figure the epineurals have their free ends swung aborad, in the 

 former figure they are swung orad. This indicates that the 

 epineural adductors were in pairs and their origins were in the 

 verv prominent, central, elongated, sunken muscle fields which 

 are so clearly shown on the oral surfaces of all adambulacrals 

 except the first of a series. The muscle pits are commensurate 

 with the size and importance of the epineurals themselves. The 

 al ductors were also probably arranged in pairs and the muscle 



