NEW GENERA OF RECENT FREE CRINOIDS 



By AUSTIN HOBART CLARK 

 Assistant, Bureau of Fisheries 



Since the publication of Dr. P. H. Carpenter's great monograph 

 on the recent unstalked crinoids in 1888, the group has received very- 

 little attention from systematists, probably because of the rarity of 

 most of the species and the difficulty in getting together representative 

 material of even the more common ones. Dr. Carpenter included in 

 the family Comatulidse the genera Thaumatocrinus, Eudiocrinus, 

 Promachocrinus (including the subsequently differentiated Decame- 

 trocrinus), Atelecrinus, Antedon, Comatula (=Actinometra) , and 

 Thiolliericrinus. All of these, with the exception of Antedon and 

 Comatula, are comparatively small, strictly homogeneous genera; 

 with them, however, the case is quite different. The genus Antedon 

 was divided by Dr. Carpenter into four "series," and all but the first 

 series into two or more "groups," the characters used in the differ- 

 entiation of the groups and series being (1) the character of the 

 joint between the costals, (2) the number of arms, (3) the number 

 of the distichals, (4) the character of the lower pinnules, (5) the 

 development or absence of covering plates on the ambulacra, and 

 (6) the rounded or "wall-sided" character of the costals and lower 

 brachials. Of all these characters, the first alone is the only one not 

 common to two or more of his series or groups, as diagnosed by 

 him. Taking No. 2, for instance, five of his groups and also several 

 unassigned species are ten-armed ; all the rest have more than ten 

 arms. A number of single species have both ten and more than ten 

 arms, as a result of purely individual variation. No. 3 is equally 

 unreliable ; some species are both ten-armed and multibrachiate, the 

 latter varieties having the distichals either 2 or 4 (3+4) ; other 

 species, very difficult to differentiate in the ten-armed varieties, be- 

 come one "bidistichate" and another "tridistichate," according to 

 species in their multibrachiate forms. In regard to No. 4, the lower 

 pinnules of the "Basicurva group" are identical in character with 

 those of the "Spinifera" and "Granulifera" groups, and those of cer- 

 tain of his heterogeneous "Milberti group" with species of the "Pal- 

 mata" and "Savignii" groups. Taking No. 5, we find covering 

 plates developed in the "Acoela" and "Basicurva" groups among the 

 ten-armed forms, and in the "Spinifera" and "Granulifera" groups 

 among the multibrachiate species ; as for No. 6, "wall-sidedness" of 



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