578 



BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



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

 develop within a marsupium 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 marsupium) one, Antedon, is an anomalous type, with 

 many oligophreate features, while the figures for the other, fLamprometra pro- 

 tectus, are of doubtful value. 



Column. In all of the comatulid larvse 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 columns!, 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 by the comatulid terminal stem plate, and with the column of 

 Thiolliericrinus. 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 : 



Promachocrinus kerguelensis 65+ 



Hathrnmetra sarsii 40-49 



Heliomctra glacialis 37-45 



Hathromctra prolixa 33-35 



tLamprom-etra protectus 33+ 



Anthometra adrlani 32 



Hathromctra tenella- 28-30 



Antedon pctaaus 27 



Antedon biftdti 16-27(20) 



Comanthus wahlbergii 17 



Comissia litt'irnlis 17 



Comactinia meridionalis 1410 



Antedon adriatica 13-18 



Antedon mediterranea 13-15 



Compsomctra lovtini 14 



Crotalometra porrecta 14 



Leptometra celtica 13 



Qlyptometra tuberosa 13 



Ptilometra miiUeri 10-12 



Tltaumatometra nutrix 10 



