54 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



6. Saccocomidae (Saccocoma). 



7. Eugeniacrinidae {Eugeniacrinus, Tetracrinus, Gammarocrinus, Gymnocrinus, 

 Phyllocrinus, Torynocrinus, Trigonocrinus, and Eudesicrinus) . 



8. Holopidae (including Cotyloderma, Cyathidium, and Holopus). 



The generic name Monachocrinus is new; the chief characters and the range are 

 given, but no species are mentioned. 



The chief feature of interest in this classification is the recognition of the fact 

 that the pentacrinites and the comatulids form two groups which are in every way 

 strictly parallel and of substantially the same phylogenetic value, though departing 

 in exactly opposite directions from the parent stock. The pentacrinites are character- 

 ized by excessive stem growth; the larval stem is lost at a very early age, but new col- 

 umnals are continuously formed with great rapidity, so that a stem of enormous 

 length results. The distal portion of this stem is continually dying away, so that the 

 actual length of the stem in any individual is but a fraction of the entire length 

 which has been formed during growth. In living comatulids the larval stem is 

 similarly lost; but after this takes place no additional columnals are formed; stem 

 growth continues within the single columnal which remains attached to the calyx; 

 this becomes greatly enlarged and puts forth numerous cirri. Comatulids may be 

 described as pentacrinites in which the entire stem is reduced or limited to the 

 compass of a single columnal, and in which the cirri (when present), unable to 

 arrange themselves in whorls on regularly spaced nodals, are closely packed together 

 on a single nodal. 



The genus Thiolliericrinus is exactly intermediate between the pentacrinites and 

 the comatuhds; the stem is developed just to the point at which the two groups diverge, 

 at that point ceasing further growth, as in the comatulids, but being retained as in 

 the pentacrinites. The structure of the stem is the same as that of the larval stem 

 of the pentacrinites and of the comatulids. 



The pentacrinites and comatulids are the dominant crinoid forms in the modern 

 fauna. The latter especially are extremely nmnerous and exist in a vast array of 

 diverse types, none of which, however, depart in any great degree from the general 

 structure of the group, so that their classification necessitates the creation of numerous 

 subfamilies, families, and higher groups which are not systematically comparable to 

 similar groups in the stalked forms. 



We were not satisfied with the disposition made of the family Plicatocrinidae, 

 which we regarded as provisional. On December 4 the present author published a 

 paper in which this family was definitely assigned to the Inadunata and placed at 

 the end of the series of families in that order, beyond the Poteriocrinidae. With 

 the addition of the Plicatocrinidae the geological range of the Inadunata is extended 

 from the Ordovician to the recent seas, in which it is the only palaeozoic crinoid order 

 still represented. Mr. Springer, in a footnote, concurred with the conclusions reached. 



An account of the recent crinoids, more especially the comatulids, in the British 

 Museum was published on December 31. The general treatment is the same as in 

 the preceding papers on the collections in European museums. 



