NO. 1668. A NEW GENUS OF UN8TALKED CRINOIDS— CLARK. 355 



weigh all the other features. The ambulacral plating is unlike that 

 developed in the Antedonidae, Tropiometridse, or Thalassometridse, 

 in that there is only a single series of plates instead of both side and 

 covering plates; these ajjpear to represent the side plates of other 

 forms, and not the covering plates, as does the single series in Rhizo- 

 crinus. The development of covering plates is an uncertain quan- 

 tity, and one upon which too much stress has previously been laid. 

 Hartlaub and Minckert both divided the old genus ^'Antedon " into 

 two sections, one with and one without them; but both included in 

 the " plated '' section Carpenter's " Basicurva group," which contains 

 sjDecies in which they are not found. Moreover, in the Tropio- 

 metrida? they are extraordinarily developed in Calomett^a, more or 

 less imperfectly developed in Asterometra and Ptilometra, and quite 

 undeveloped in Tropiometra; but more curious still, while they make 

 their appearance in the pentacrinoid stage of the species of Thalasso- 

 metrida3, they are not found in the young of Ptilometra. It is evi- 

 dent, therefore, that, though a valuable index to the systematic posi- 

 tion of the comatulid species, they must be treated with great cau- 

 tion, as they apj^ear to be very liable to sudden development, as is the 

 case in Heliometra^ in very unexpected places, and to equally dis- 

 concerting suppression. The central position of the mouth, while 

 interesting, is of no real importance; it is usually nearly, and often 

 quite, central, in Phanogenia, Comatella, and Comaster^ and often 

 more or less eccentric in Heliometra and in certain of the Himero- 

 metridse. Sacculi are somewhat uncertain organs at best, while cirri 

 are so very variable that the occurrence of a new type need cause no 

 trouble; the resemblance to the cirri of Iridometra is not borne out 

 by the finer structure; for instance^ in Iridometra^ as in all comat- 

 ulids heretofore known, the opposing spine is single, whereas in this 

 new form it is forked. 



I propose to recognize this new comatulid as follows : 



Genus COMATILIA, new. 



Centro-dorsal discoidal, moderate in size; cirrus sockets marginal, 

 usually in a single rowi 



Cirri about XX, 9-10, about one-fifth of the arm length, very 

 slender, the second and following joints much longer than broad, the 

 third and fourth the longest, about four times as long as their prox- 

 imal diameter; cirrus joints all with expanded ends; no dorsal spines; 

 opposing spine forked in its distal half, or ending in a bunch of fine 

 spines. 



Arms 10; first four brachials oblong, broader than long, then ob- 

 liquely wedge-shaped, at first as long as broad, soon becoming longer 

 than broad and very long terminally; large interprimibrachs present, 

 rounded, not contiguous. 



