144 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



simulated by the teeth in the pedicellaria; of many echinoids and a few starfishes. 

 But there is no reason to assume a direct genetic connection between these struc- 

 tures. A comblike arrangement of processes occurs in certain worms, on the 

 mandibles and other appendages of many crustaceans, on the posterior legs of 

 certain spiders, on the anterior legs of the male of the fruit-fly {Drosophila) , on 

 the antenna; of many insects, particularly among the Coleoptera and Lepidoptera, 

 and on the middle toe of certain goatsuckers of the family Caprimulgidse. 



On the undivided arms the species of Comasteridse commonly possess two pairs 

 of true oral pinnules (figs. 262. 265, p. 207), succeeded by a pair of pinnules inter- 

 mediate between oral and genital pinnides, though nearer the former. 



Comatilia, which is the only comaterid with deficient pinnulation, has only a 

 single pair (fig. 264, p. 207) ; but the next three pairs of pinnules are absent. 



In the 10-armed genus Co-matonia the combs are confined to Pj and Pa and are 

 not always developed. When present they arise at about, or even within, the 

 proximal third of the pinnule, and are composed of exceptionally large rounded 

 teeth, which usually much exceed in height the lateral diameter of the segments 

 which bear them. This genus is also unique in having one or more of the earlier 

 segments of P, twice as long as broad, or even longer. Furthermore, it is the only 

 comasterid which possesses numerous large and conspicuous sacculi. 



Usually in the Comasteridse the oral pinnules, in correlation with their much 

 greater length, are stouter basally than those following, though they taper rapidly 

 and soon become very slender. But in some forms thej' are but very little longer 

 than those succeeding, and in these they are much more slender with shorter 

 segments. 



Except for the characteristic terminal comb the oral pinnules of the Com- 

 asteridse are comparable to those of such macrophreate tj'pes as the Heliometrinse 

 (figs. 292-294, p. 221) and the Thysanometrinse (figs. 282, p. 215, and 298, p. 221), 

 and to those of the Pentametrocrinidse (fig. 286, p. 215, and part 1, figs. 119, p. 185, 

 120, p. 187, and 121, p. 189) ; their general development is along the lines followed 

 in these groups rather than along the lines followed in the other families of the 

 Oligophreata. 



The rudimentary comb developed in the Heliometrinse (figs. 1053, 1054, pi. 13) 

 is a production of the entire distal surface of the outer pinnulars instead of a thin 

 outgrowth from one border of the distal surface, and there is never any basal con- 

 striction to be seen in connection with it. It may best be described as a blunt 

 carination of these ossicles, in its most developed form more pronounced externally 

 than internally, and seems to be the result of the lateral compression of the pinnule 

 tip instead of the expression of a tendency toward a prismatic development as is 

 the comb of the Comasteridse, which is always accompanied by more or less exca- 

 vation of the distal surface of the segments. 



Almost all of the species which compose the families treated above have the 

 oral pinnules transformed into organs of touch. Among the majority of the 

 species of the Himerometridse (figs. 268, 269, p. 207), Stephanometridse (fig. 310. 

 p. 223), Mariametridse (figs. 312, 313, p. 223) Colobometridse (figs. 274, 278, p. 213), 

 and Calometridas (figs. 314, 320, p. 227, and 311. p. 223), while the first pair is thus 



