THE OTTAWA NATURALIST 



Vol. XXVI. DECEMBER, 1912 Xo. 9 



ON THE NATURE OF THE SO-CALLED "COVERING 

 PLATES" IN PROTOPAL.-EASTER NARRAWAYI. 



By Percy E. Raymond. 



In the autumn of 1910, Mr. J. E. Narraway, of Ottawa, 

 found a small starfish in the Black River limestone at City View, 

 a short distance west of the Central Experimental Farm at Ottawa. 

 On examining the specimen on his return from the field he 

 found that the central groove in two of the rays was roofed over, 

 for a short distance, by flat, alternating plates which met on 

 the median line and formed a tight, tent -like covering over the 

 groove. Furthermore, these plates were borne by two rows of 

 small plates just inside the marginal series, and each plate was 

 provided with a cup-like pit into which the proximal end of a 

 covering plate fitted. The specimen had every appearance of 

 being exposed from the actinal side, and assuming that such 

 was the case, the plates were interpreted as being homologous 

 with the covering pieces over the ambulacral grooves of cystids 

 and crinoids. Mr. Narraway at once drew the writer's attention 

 to the specimen, and I fully agreed with him as to its* nature 

 and importance. It was next shown to Professor Hudson, 

 whose work on Ordovician echinoderms is well known. He 

 concurred in our views of the specimen, which he studied with 

 great care, and he finally described and figured the species in 

 The Ottawa Naturalist for May and July, 1912. Before the 

 publication of his paper, photographs and descriptions had 

 been seen by three or four paleontologists and students of recent \ 

 echinoderms, and, it must be confessed, all dissented from our 

 view as to the nature of the "covering pieces." 



Recently, in searching the collection of starfish in the 

 Museum of Comparative Zoology. Cambridge, Mass., the writer 

 came upon what seemed to be a second specimen showing the 

 "covering plates." (See plate VI, fig. 1). This specimen has three 

 imperfect arms, all of which show the groove covered by alter- 

 nating plates which are obtusely pointed at their distal ends, 

 where they fit together closely. Some of the plates have been 

 removed from portions of the arms, and it is then seen that the 



