A. H. CLARK: THE CRINOIDS OF THE INDIAN OCEAN. 43 



Atlantic forms. Many of the Atlantic genera are very close to the corresponding 

 East Indian genera, and their inchision in these keys, while serving no useful 

 purpose, might lead to considerable confusion. 



9. EXPLANATION OF TERMS. 



In the description of a comatulid the number of the cirri is expressed by 

 Roman numerals, and the number of their component segments by Arabic; thus 

 "cirri XVII, 25" means that the animal has seventeen cirri, each with twenty- 

 five segments. 



The division series are indicated by the letters " Br, " preceded by the num- 

 ber of the series; thus " IBr" means the first division series following the radials, 

 the "costals" of P. H. Carpenter's terminology in his later works, and the 

 "second and third radials" of the "Challenger" reports; "IIBr" is equivalent 

 to " distichal series," " IIIBr " to "palmar series," "IVBr" to "post-palmar 

 series," etc. The individual elements of the division series are indicated by so- 

 called inferior numbers; thus IIBr, means the first distichal, or the first ossicle 

 of the second division series. 



The presence of a syzygy is indicated by the use of the symbol " -j- "; thus 

 IIBr 4 (3+4) means that the second division series, the " distichals, " is composed 

 of four ossicles of which the third and fourth are united by syzygy. In the 

 " Challenger" report this is expressed as "three distichals, with a syzygy in the 

 axillary." 



The outer pinnules of an arm are numbered in regular sequence, P,, P.^, P^, 

 etc.; the inner pinnules are lettered P„, P4, P^, etc. The IBr, or ''costal," 

 pinnule (only found in the genus Eudiocrinus) is given as Pq, the IIBr, or " dis 

 tichal," pinnule as P^, and the IIIBr, or "palmar," pinnule as Pp, the use of 

 these inferior capitals serving to differentiate these pinnules from those of the 

 inner side of the arm. 



1. — Key to the Suborders of the Comatulida.' 

 a' Cavity in the centrodorsal containing the chambered organ and overlying struc- 

 tures very small; both the radial and interradial processes of the rosette 

 form " spout-like " processes; rosette sunk below the level of the dorsal surface 

 of the radials; pinnules, at least the proximal, wholly or in part prismatic, and 

 composed of short segments ; the post-radial series usually divide two or more 



times. 



Comatulida Oligophreata, p. 68. 



(C/. keys 2—5; 7—18.) 



' In the following keys the oligophreate families are not kept separate from the macrophreate , 

 but all the families are considered as if belonging to a single suborder. This renders accurate iden- 

 tification much more easy, as in many cases, while the family characters are prominent, the subor- 

 dinal characters are very obscure. The family names in the keys are preceded with the letters " O " 

 or "M" in parentheses, signifying to which of the suborders they belong, so that an individual 

 whose family rank is determined may be readily tested in the key to the suborders. 



