584 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



or more. It is largest in the species with conical centrodorsals, the species of 

 Heliometra, Promachocrinus, Anthometra, and Hathrometra, in which also the 

 crown is most developed at the end of the pentacrinoid stage, and in which the 

 length of the larval life appears to be longest. 



Infrabasals. Unless sufficient material is available representing the very 

 early stages, which is very rarely the case, the presence or absence of infrabasals 

 in pentacrinoids is very difficult to determine. 



There are five infrabasals in 



>Ptilometra rrvulleri. Antedon adriatica. 



Promachocrinus kerguelensis. 



There are three infrabasals in Antedon mediterranea. 



There are no infrabasals in 



C'omactinia meridionalis. Antedon bifida. 



Antedon petasus. Heliometra glacialis. 



Hathrometra prolioca. 



The presence or absence of infrabasals has not been definitely determined in 



CotnissM littoralis. Compsometra loveni. 



fLamiprometra protectus. Leptometra celtica. 



Crotalometra porrecta. Anthometra adriani. 



Glyptometra tuberosa. Hathrometra tenella. 



Hathrometra sarsii. 



Judging from the figure given by P. H. Carpenter there would appear to 

 be large infrabasals present in Leptometra celtica, ; such an interpretation, however, 

 is open to question. 



Basals. The basals exhibit relatively little variation. 



In the Oligophreata and in Antedon the basal cup is relatively broad from its 

 first appearance, while in the Macrophreata it is narrower and appears elongated, 

 being about as long as its distal diameter. In the later stages this difference usually 

 disappears. 



At first all the basals are of the same size and symmetrical, but in the later 

 stages the left distal border of the posterior basal becomes longer than the right. 

 The difference is usually not marked, but in Anthometra adriani it is very pro- 

 nounced, the left distal side of this basal being from half again to twice as long 

 as the right. 



The condition of the basals at the time of the loss of the column varies greatly, 

 being correlated with the comparative state of development of the crown in other 

 respects. In those species in which separation from the larval stem occurs rela- 

 tively early when only a few cirri are developed on the centrodorsal the basals are 

 still of considerable size and very noticeable in an external view, while in those 

 species in which the crown is well advanced and numerous cirri and pinnules are 

 developed they are completely concealed by the centrodorsal. 



Radials. The development of the radials follows the same course in all types. 



There is a great difference in the relative time at which the two posterior 

 radials come into contact beneath the radianal, but this is dependent upon the 

 development of the latter and is only secondarily an attribute of the radials. 



