362 PR0CEEDIN08 OF THE NATIONAL MUSEUM. vol. xxxvi. 



which, judged upon its other characters, might be placed in the 

 Antedonidse, Himerometridse, Thalassometridse, or Tropiometridse, 

 while certain features find a parallel only in Rhizocrinus and Batliy- 

 crinus. Briefly stated, the essential features of the Comasteridie are, 

 an eccentric mouth, large central or subcentral anal tube, ambulacra 

 quite without calcareous plating, absence of sacculi, stout cirri with 

 short joints, and the full complement of pinnules, the lowest of which 

 bear terminal combs. The first and the last are the characters upon 

 which most reliance is usually placed. In this new form the mouth 

 is always central, the anal tube small and marginal, sacculi are pres- 

 ent (though rare), the cirri are exceedingly slender, with greatly 

 elongated joints, the six pinnules following the first two (P^ and Pa) 

 are lacking, the pinnule ambulacra are provided with large side 

 plates, and the two lowest pinnules are combed. In its central mouth 

 this new species agrees with all the other recent species except those 

 of the Comasterida\ and the same is true in regard to the sacculi ; 

 the delicate cirri find counterparts only in the Antedonidee, in the 

 genera Hathrometra and I ridometra ,' the deficient pinnulation recalls 

 Perometra and Tlypalometra among the Antedonidae, CyUometra and 

 Colohometra among the Himerometrida» (with this exception, that 

 the first inner pinnule, on the fourth brachial. Pa, is always the first 

 to disappear in these genera, while it is invariably present in the 

 new form), and also Atelecritnis of the Atelecrinida^; the develop- 

 ment of an ambulacral plating is found perfected only in the Thalas- 

 sometrida^ and in the Tropiometridse. Taken as a whole, the great- 

 est resemblance in size and general build is to the little littoral 

 Antedonids of the East Indies belonging to the genus Iridometra, 

 I. nana in particular, and this in spite of the fact that it has the 

 deepest habitat of any of the Comasterida\ 



The development of plating along the ambulacra in the family 

 Comasterida^ was first demonstrated by Mr. Frank Springer, who 

 showed its presence in a new species of Comaster, C. iowensis, from 

 the Tortugas. I have since found it to be a constant feature of the 

 AVest Indian species of this genus, even including C. lineata, in which 

 I detected it in specimens previously examined by Carpenter. 



No less interesting than the adults are the young, as shown by a 

 single specimen with an arm length of probably about 7 mm. Had 

 it not been found with the fully grown, it could very well have passed 

 as a new species of Thaumatocrinus, or the representative of a genus 

 intermediate between Thaumatocrinris and Antedon. 



Thaumatocrinus renovatvs was based upon a very peculiar coma- 

 tulid which had been dredged by the Challenger in 50° 01' S. lat., 

 128° 04' E. long., at a depth of 1,800 fathoms. Doctor Carpenter's 

 diagnosis of the genus, as given in the Challenger Reports, is : 



Calyx composed of a centro-dorsal, basals, radials, and primary 

 interradials, the latter resting on the basals and so separating them 



