MONOGRAPH OF THE EXISTING CRINOIDS. 41 



Carpenter did not subdivide the genera Antedon and Actinometra, but he 

 arranged the species in a number of more or less well defined groups for the better 

 appreciation of their differential specific characters (but not of their specific inter- 

 relationships), as follows: 



Antedon. 



Series I. The two outer radials united by syzygy. (This includes only the 

 "Elegans group"; Carpenter did not employ this name in the Challenger 

 report, introducing it for the first time in his report on the comatulida of 

 the Mergui Archipelago, 1889.) 

 Series II. The two outer radials articulated; 10 arms. 



The radials and lower brachials have flattened sides; pinnule ambulacra 



generally plated 1. "Basicurva group." 



The rays not flattened laterally. Pinnule-ambulacra well plated 2. "Acoela group." 



The first two or three pairs of pinnules long and flagellate, with numerous 



short and wide joints 3. "Eschrichti group." 



The joints of the lowest pinnules, which are often long and slender, are 



longer than wide, frequently very much so 4. "Tenella group." 



The first pair of pinnules is comparatively small, and their joints but 

 little longer than wide; one or more of the second, third, and fourth 

 pairs are longer and more massive, with stouter joints than their suc- 

 cessors 5. "Milberti group." 



There are in addition six lO-armed species which Carpenter does not assign to 

 any of the preceding groups. 



Series III. Two articulated distichals. 



Bidistichate species with the radial axillaries and some of the following 

 joints more or less wall-sided, and a well marked ambulacral skeleton 

 on the pinnules 6. "Spini/era group." 



Bidistichate species with an unplated disk and no definite ambulacral 

 skeleton. The sides of the lower brachials are scarcely, if at all, 



flattened. The first pinnule smaller than its successors 7. "Pa^/nata group." 



Series IV. Three distichals, the first two articulated, the third axUlary with a 



syzygy. 



Tridistichate species with plated ambulacra and the lower parts of the 



rays flattened laterally 8. "Granulifera group." 



Tridistichate species with an unplated disk and no definite ambulacral 



skeleton; the bases of the rays are not flattened laterally 9. "iSoCTjnyi group." 



Actinometra. 



Series I. The two outer radials and the two first brachials respectively united 

 by syzygy. 



Ten arms 1. "Solaris group." 



Two distichals, united by syzygy 2. "Paxtcicirra group." 



Three distichals, the axillary a syzygy 3. "Typica group." 



Series II. The two outer radials articulated; 10 arms 4. "Echinoptera group." 



Series III. Two articulated distichals. 



Two articulated distichals. The palmars and subsequent series, when 

 present, are of the same character; but the first two brachials are 



united by syzygy 5. "Stelligera group." 



Two articulated distichals; the first arm syzygy in the third brachial 6. " Valuia group." 



79146°— Bull. 82—15 i 



