578 



BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



It must be remembered that in those macrophreate species in which the larvae 

 develop within a marsiipium the column of the pentacrinoids is short, as in the 

 Oligophreata. 



The percentage of the total length represented by the crown varies very greatly, 

 as is evident from the following table : 



From these figures it appears that in the Oligophreata the columns of the 

 pentacrinoids are relatively much shorter than in the Macrophreata, ranging from 

 46.6 to 66.6 per cent of the total length, as against 19.2 to 29.4 per cent in the latter. 

 Of the two exceptions to this generalization (outside of the forms in which the 

 young develop within a marsvipium) one, Anfedon, is an anomalous type, with 

 many oligophreate features, while the figures for the other, fLampro'metra jn-o- 

 tectus, are of doubtful A'alue. 



Column. — In all of the comatulid larvte the stems are of exactly the same 

 type. At the summit there are a few discoidal or lenticular, very short, segments, 

 usually decreasing slowly in diameter, after which the columnals, becoming cylin- 

 drical, rapidly increase in length, at about the middle of the stem becoming 

 constricted centrally with expanded ends, the articular faces of which, oval in out- 

 line, are at right angles on the two ends of each columnal, and toward the distal 

 end becoming shorter again. 



The larval column of the comatulids is the exact counterpart of the very young 

 sections of the pentacrinite stem, if we assume one of the lowest of the pentacrinite 

 nodals to be replaced bj' the comatulid terminal stem plate, and with the column of 

 T/doUier-icr-mus. It differs from that of the Bourgueticrinidse, aside from the 

 development of the proximale into a cirriferous nodal, in lacking the occasional 

 union of the columnals in syzygial pairs, which is so conspicuous a feature of the 

 younger portion of the column in the recent types. 



The number of the columnals in the pentacrinoids of the comatulids is as 

 follows : 



Promochocrinua kerguelensis 65-|- 



flathroiiietra sarsii 40-49 



Helinmctra glacialis 37—45 



Hathromctra jiroHxa 33-35 



tLamprometra protectus 33-1- 



Anthomctra adriani 32 



Hathrometra tenella- 28-30 



Ante,(1on petasus 27 



Anterton bifida 16-27(20) 



Comanthus tvablbergii 17 



Comissia littoralis 17 



Comactinia 7»eridionalis 14—16 



Anteilon adriatlra 13-18 



Antedon mediterrnnea 13-15 



C'ompsnmctra lov6ni 14 



CrntaloDietra porrecta 14 



Le^ptonxtra celtica 13 



Olyptometra tvhcrosa 13 



Ptilometra miilleri 10-12 



Thaumatometra vutrix 10 



