no. 1636. ARM HOMOLOGIES IN RECENT CRINOIDS— CLARK. 123 



In Comaster marice, 0. flmbriata, 0. coppingeri, C. borneensis, 0. 

 multiradiata, C. iowensis, C. sentosa, C. lineata, and G. discoidea (fig. 

 24), and in a number of undescribed species from the West Indies, 

 we find a somewhat anomalous condition; the second post-radial divi- 

 sion consists of four joints, 4 (8+4) ; but the next joint succeeding 

 the second post-radial axillary bears a pinnule, whether it be the first 

 joint of another division series or the first joint of an undivided arm; 

 in other words, all the joints following the second post-radial axillary 

 are pinnnlate. except of course, the axillaries. It is at once evident, 

 then, that the first joint in the free undivided arm can not be Z 15 for it 

 bears a {oblique) muscular articulation instead of a von muscular 

 articulation distally. Where, then, is Z x ? The articulations subse- 

 quent to the first post-radial axillary are, straight muscular articula- 

 tion, by which the first post-radial axillary articulates with the next 

 succeeding joint, synarihry connecting that joint with the next; 

 oblique muscular articulation, syzygy, and, on the distal faces of the 

 axillary, oblique muscular articulations. By the application of our 

 definition, we find that Z t and Z 2 are the first and second joints fol- 

 lowing the first post-radial axillary, instead of the first and second 

 joints of the free undivided arm, as we found in all cases heretofore. 

 The axillaries and division series subsequent to the first post-radial 

 axillary are, therefore, not morphologically homologous with the first 

 division series, and the division series in all the other forms which we 

 have considered, although, of course, they are physiologically analo- 

 gous. We may designate the division series formed by the presence 

 of repetitions of Z 1 and Z 2 interposed between the primitive Z x and Z 2 

 and the radials as interpolated division series, while division series 

 formed by a splitting of the arm at a certain joint, which therefore 

 becomes an axillary, may be called extraneous" division series. 



It seems to me that such a radical departure from the ordinary 

 comatulid type of interpolated arm division occurring in a group of 

 species entitles them to recognition as a valid genus, more especially 

 as Metacrinus has been separated from Isocrinus along exactly sim- 

 ilar lines; and, since a generic name has been based on a species in 

 each group of the genus Comaster, I propose to reinstate Loven's 

 name Phanogenia, and to consider the family Comasterida? to be 

 naturally divisible as follows: 



a 1 . Synarthries all replaced by syzysies Comatula ( ti.^s. 21, 22. and i!."'.) 



a 2 . Synarthries present between the first two post-radial joints. 



b\ interpolated arm divisions throughout Phanogenia < fig. 20) 



If. first arm division interpolated, all following extraneous Comasteb ( lii.'. 24) 



° From extraneus, external (in reference to Zi and Z a ) as opposed to inter- 

 polated (between tbe radials and Zi). 



