48 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



also bearing in mind the more or less strong reduction of the proximal pinnules, Gislen 

 proposed the new generic name Seirocrinus for Pentacrinus subangularis and its imme- 

 diate relatives. 



Gislen said it is evident that the hypothetical ancestor of the comatulids unites in 

 itself characters belonging to both Seirocrinus and Pentacrinus, sensu stricto. It 

 approaches Pentacrinus in its short stem consisting, after the development of the 

 first nodal, of nodals only, as well as by the strong cirri. He said that among known 

 forms Pentacrinus dargienesi comes nearest to the comatulids. The stem did not 

 reach more than 60-70 mm. in length, while the cirri were 100 mm. long. The comat- 

 ulids approach Seirocrinus through the defective pinnulation that appears in their 

 ontogeny, which probably, in Gisle'n 's belief, is caused by the perisome once having 

 swelled out between the arms. 



Gislen noted that it is not only among the Articulata discussed above that a gap 

 in the proximal pinnulation occurs. Among recent forms pinnule gaps appear in the 

 adults of various stalked types. They are met with throughout the Bathycrinidae. 

 In Bythocrinus the first pinnule appears on from the fourth to the twelfth brachial 

 (in Bythocrinus cf. braueri on the fourth to the sixth brachials; in B. braueri on the 

 eighth; and in B. chuni on the tenth to twelfth) ; in Democrinus (rawsonii and weberi) 

 the lowest pinnule is on the sixth brachial; in Rhizocrinus (lofotensis) it is on the eighth; 

 in Bathycrinus it is found on from the eighth to the tenth (in Bathycrinus pacificus on 

 the eighth; in B. aldrichianus on the ninth; and in B. serratus on the ?tenth); in Ily- 

 crinus it is found on from the ninth to the ?twelfth (in Eycrinus australis, ninth to 

 eleventh;/, carpenterii eleventh or twelfth; and in /. complanatus, tenth to twelfth); 

 and in Monachocrinus (sexradiatus) it is found on from the tenth to fourteenth. In 

 the Phrynocrinidae only the arms of Phrynocrinus nudus are known. The first 

 pinnule appears here on the eighth brachial. In the Hyocrinidae also a proximal 

 pinnule gap is found, as one pinnule to the right and one to the left is lacking. The 

 first pinnule therefore appears on from the fourth to the sixth brachial, the variation 

 being due to the difference in distribution of the syzygies. 



Gislen said that if his idea that the bathycrinids are derived from the Bourgue- 

 ticrinidae and the latter are descended from a form nearly related to the comatulids 

 and thiolliericrinids is correct the explanation of the pinnule gap in the bathycrinids 

 will be the same as that given in the case of the comatulids. The disk in the bathy- 

 crinids of the recent seas does not reach far up on the arms in Rhizocrinus, with 5 

 arms, to the second brachial, and in Ilycrinus with 10 arms also to the second brachial 

 (fourth postradial ossicle). Gislen said it seemed to him in many cases as though 

 this may be explained partly by the disk having sunken in between the greatly elon- 

 gated basals (in Bythocrinus, Democrinus, and some species of Monachocrinus). 



In Phrynocrinus the very large disk reaches up to about the twentieth brachial. 

 The disk and arms of Naumachocrinus are not known; in this genus the radials are 

 greatly elongated. 



A high disk is also found in certain of the Hyocrinidae. In Ptilocrinus, in which 

 it extends to the sixth brachial, the arms are grown fast together as far as the fifth 

 brachial. In Calamocrinus, in which the disk is connected with the arms up to the 

 ninth or tenth brachials, the anal tube reaches to the IIBr 3 (the axillary tenth post- 



