Clark — New Genera of Unstalked Crinoids. 135 



crinus and Thaumatrocrinus , the costals* are absent, and the first post- 

 radial joint is the first brachial. As an item of considerable interest it 

 may be mentioned that in these species of " Eudiocrinus, " in Decametro- 

 crinus, Thatnnatocrinus, and Uintacrinus, the first syzygy is between the 

 fourth and fifth brachials, not between the third and fourth as is com- 

 monly the case; in analyzing the arms of Uintacrinus* it must be remem- 

 bered that there are two distichals present, of which the second is not 

 an axillary, so that the first brachial is the third joint from the costal 

 axillary. 



The genus Pentametrocrinus, as here defined, contains the following 

 species : 



P. atlanticus (Perrier). P. semperi (P. H. Carpenter). 



P. japonicus (P. H. Carpenter). P. tuberculuttts (A. H. Clark). 



P. varians (P. H. Carpenter). 



Some time ago I proposed the family Eudiqprinidse to cover these 

 species and Decametrocrinus, not being aware at the time that Eudio- 

 crin us indivisus was so radically different. Eudiocrin us as here restricted 

 belongs to the family Zygometridae with the genus Zygometra, while 

 Pentametrocrinus and Decametrocrinus may be united under the family 

 name of Pentametrocrinidas, which is the exact equivalent to what I 

 intended by my " Eudiocrinidse. " Minckert's family "Decametro- 

 crinidse" must be rejected, it being composed of Promachocrinus, a 

 genus of Antedonidse very near Heliometra, and the utterly different 

 Decametrocrinus. 



The arm structure of Thaumatoerinus suggests that in reality it belongs 

 to the Pentametrocrinidse, near Pentametrocrinus. 



The genera of free crinoids belonging to the Comatulida may be grouped 

 as follows, the most specialized types being placed first. 



Family UJNTACRINID.E. 



Uintacrinus. 

 Family COMASTERID.E. 

 Comatula. Co-master. , 



Family ZYG< (METRIDJv 

 Eudiocrinus. Zygometra. 



Family HIMEROMETRID.E. 

 Himerometra. Cyllometra. 



Pontiometra. Oligometra. 



Family TROPIOMETRID^E. 



Tropiometra. Calometra. 



Asterometra. Ptilometra. 



* The costals are, in reality, merely repetitions of the two first brachials of the free 

 arm interpolated between the regular first brachials and the radials; the distichals and 

 palmars are additional reduplications of the two first brachials, either single (2) or 

 double (4[3 + 4] or 4 [1 + 2; 3 + 4]), the two pairs in this latter case being separated by 

 a muscular articulation like that at the distal end of all costal and division series. 



