8 TH. MORTENSEN, (Schwed. Südpolar-Exp. 



presence of a pore in the dorsal pole of the centrodorsal until a late stage of age. 

 Likewise the retention of the anal plate and occasionally of the oral plates; further 

 the presence of externally visible basalia is decidedly a primitive feature. 



The pore in the dorsal pole of the centrodorsal, as is well known, generally re- 

 mains only for a short time after the detachment from the stalk of the young Crinoid. 

 P. H. Carpenter ('Challenger« Comatulidîe, p. 7 — 8) calls attention to the presence 

 of a corresponding opening in the centrodorsal of some fossil Comatulids, regarding 

 it as a larval character preserved in adult life. A. H. CL.A.RK in his Monograph of 

 the E.xisting Crinoids ■ ' is firmly of the opinion that it is a purely secondary feature, 

 produced after death by the erosion of the dorsal pole ■. . . . 'There is no reason 

 whatever for supposing that the centrodorsal in any fossil species was open at the 

 dorsal pole any more than it is in any recent species, and there is no evidence which 

 undeniably supports such a view." The present case undeniably supports Carpenter's 

 view. There is not the slightest indication of any erosion of the centrodorsal in 

 Notocriuiis, and the fact that the pore disappears in full grown specimens is evidence 

 enough, that we have here a ='larval- — or, in any case, a primitive — feature pre- 

 served until a much later stage than is the case in other Comatulids, so far as known, 

 and it probably means that the larval stalk is preserved until a correspondingly late 

 stage. The exceptionally large size of the embryos may have something to do 

 with this. 



Concerning the basalia the question remains to be discussed, whether they are 

 really true basalia and not basal rays. The decision of this question is by no means 

 easy, the only definite critérium lying in the development of these skeletal pieces, 

 the basal rays being, as ascertained by P. H. CARPENTER," calcifications in the syn- 

 ostosis between the centrodorsal and the radiais, tertiary elements of the compound 

 basal structure. Of course, there is no possibility of following their development in 

 NotocriiiHS on the material available; however, I venture to maintain that they are 

 true basalia alone from the fact that the rosette is of a very primitive structure: a 

 simple, fairly thick plate without any of the usual processes (PI. II, Fig. 2). This 

 fact combined with the other primitive features, the persistence of the central pore 

 and of the anal plate, are decidedly against regarding the said structures as basal 

 rays, which would mean an enormous development of this very specialized feature, 

 in the same time as other important structures remain in a primitive condition. 



Furthermore, I would confess, that I do not feel at all convinced that CARPENTER 

 (whose views are adopted by A. H. Clark) is right in his statements regarding 

 the development of the basal rays. That calcification of a fibrous tissue is, on histo- 



• Bull. U. S. National Museum 82. 1915, p. 22S. 



^ P. H. Carpenter. Oq the genus .^ctinometra. Trans. Linn. Soc. II. Ser. Zoology. Vol. II. 

 1S79, ?• 95—104- 



