ON SOME PELMATOZOA FROM CHAZY LIMESTONE OF NEW YORK IIO, 



plates, and its food grooves with their covering pieces leading to 

 the mouth. 



We must not make too much of the absence of true brachials. 

 The primary meristem in our species has already formed just such 

 a linear series of single plates (the wing plates) on the upper sur- 

 face of a ray. Does this radial series of single large plates give 

 an excuse for the announcement of a new class of Echinoderms 

 separate from all others? We may imagine our primary meristem 

 to start a new wing plate and then push up between it and the last 

 formed. This would give an outer brachial to a now ascending uni- 

 serial arm. It would also require but a slight modification of the 

 structures formed by this meristem to produce an ascending biserial 

 arm with its fringe of pinnules. The ascending arms would at once 

 retire the tegmenal brachioles from service and the modification or 

 loss of these and adjacent structures would follow. In my description 

 of Carabocrinus geometricus, 1 ' I suggested that the 

 tegmen had plates bordering the lateral sides of the deltoids and thus 

 underlying the food grooves. Figure 2, plate I, of that report would 

 suggest such a condition but the figure does not do justice to the 

 specimen. The notches for the bases of the deltoids are more regu- 

 lar than in the figure and the angles at the corners should have their 

 outer sides running parallel with the lines taken by the missing food 

 grooves. These bordering plates might be homologous with the 

 adambulacrals of Blastoidocrinus. 



The affinities of this genus seem to associate it most clearly with 

 the Blastids but under neither grade as defined by Bather. I pro- 

 pose a new order for this genus under the name of Parablastoidea 

 and with the following characters. 



PARABLASTOIDEA 



Blastoidea with the theca more or less clearly separable into an 

 oral and aboral surface. The aboral consists of three or more 

 circlets of plates. Basals (unknown) ; five radials, in contact all 

 around ; five pairs of plates over the radials and supporting the 

 distal ends of the ambulacra (bibrachials of Blastoidocrinus), and 

 between them and completing the third circlet a group of smaller 

 plates (interbrachials of Blastoidocrinus) arranged in one or 

 more transverse rows. The oral surface possesses normally five 

 ambulacra without a lancet plate but with adambulacrals meeting 

 under the food grooves, with covering plates and with numerous 



X N. Y. State Pal. An. Rep't. 1903. p. 282. 



