Catalogue of the Blastoidea. 



421 



the basal cup is elongated and tapers elegantly downwards until its 

 narrow lower end rests directly upon the first stem-joint, which is 

 sometimes seen still united to the base. One Pentremite has been 

 obtained by Mr. Wachsmuth, in which the stem terminates below 

 in a branching root like that of the Bonrgueticrinidce : whilst three 

 genera of Blastoids, namely, Pentephyllum, Eleutherocrinus, and 

 Astrocrinus. appear to have had no stem in the adult state, whatever 

 may have been the case during their early life. 



The following definition of the Pelmatozoa 1 (under which name 

 the stalked Echinodermata are classed by the authors) will probably 

 give the leading characters of this difficult group more clearly than 

 any words of our own : — 



" Phylum Echinodermata, Branch Pelmatozoa. Echinoderms 

 which are fixed either permanently or temporarily by the middle of 

 the aboral surface. A jointed stem containing a neuro-vascular axis 

 is usually present, but may be lost when maturity is reached ; or, in 

 the case of a few sessile forms, remain altogether undeveloped. The 

 apical system consists of a dorsocentral plate, basals, and radials, 

 with the frequent addition of under-basals and interradials. These 

 plates form a cup, which either simpty supports, or more or less 

 completely encloses, the visceral mass, and often bears jointed 

 appendages — the arms and pinnules. 



A. B. 



Fig 1'.— Diagram of Troostoerinus Reinwardti. A. the anal side. B. the summit 

 view. The radio-deltoid sutures are shown hy rather darker lines. 



"An oral system, which is to some extent a repetition of the apical 

 system, and consists of a central plate, basals, radials, and inter- 

 radials, is developed to a very variable extent above the actinal sur- 

 face of the larva. It may be (1) altogether resorbed ; (2) persist as 

 basals only which cover the peristome ; or (3) reach a high state of 

 development so as to form a complex vault or tegmen calycis covering 

 in the whole visceral mass. The anal tube opens on the oral surface, 

 but is sometimes in close relation with the calyx-plates. 



" The water- vascular ring does not communicate directly with the 

 exterior, and the lateral branches of the radial vessels (when present) 

 are respiratory, but not locomotor in function." 



1 From 7re'A/ua, ireA^toTos, stalked, and (Hov, animal. 



