MONOGRAPH OF THE EXISTING CRINOIDS. 209 



In practically all species of comatulids the distal dorsal border of the brachials 

 is more or less produced outward over the base of the succeeding segments (figs. 

 1059. pi. 14, and 1070, pi. 15), and at the same time is more or less spinous or sharply 

 dentate. This character appears in the young not long after the beginning of the 

 free existence. It is primarily the result of the cessation in the longitudinal growth 

 of the ossicles, due to the development of the articular faces and the fixation of the 

 organic matter in a more or less stable form before the deposition of calcareous 

 matter has ceased an expression on a small and limited scale of the well-recognized 

 fact that skeletal structures continue to develop after the other structures have 

 reached maturity the further calcareous deposition taking place at the only point 

 possible, the free distal edge of the ossicle bordering the dorsal ligament fossa. 



As a rule the production of the distal edge of the brachials is not evident 

 proximal to the fourth brachial of the free undivided arm, gradually increasing in 

 intensity from that point outward, but diminishing again near the tip. 



The distal edges of the pinnulars, except the first two, are almost always pro- 

 duced and spinous, like the distal edges of the brachials, and this feature increases 

 from the base of the pinnules outward. 



In the cirri spinous distal edges on the segments are not common. They occur 

 in the species of the genus" Colobo??ietra and in a few of the species of Thalasso- 

 metra, where they are developed on the basal segments and extend outward in 

 diminishing intensity onto the fixed proximal segments. They never occur on the 

 mobile outer cirrals. 



In the Macrophreata the production of the distal dorsal edges of the brachials 

 and of the pinnule segments is always very slight, though always present, at least 

 distally. It is sometimes reduced to a row of fine spinelets, which are scarcely 

 visible even under a good glass. In the Oligophreata it is always pronounced and 

 is often carried to extremes, as in the Comasteridse, especially in the species of 

 Comaster and in certain species of Comanthus, in most of the species in the Zygo- 

 metridse, in many of those of the Himerometridffi, Mariametridse, Charitometridse, 

 and Thalassometrinse, and particularly in the genus Colobometra. 



This produced distal dorsal edge of the ossicles is always serrate for the 

 reason that all free calcareous borders of crinoid ossicles increase by sending out 

 more or less slender and tapering teeth, as is well seen in the development of the 

 orals. With further growth the interstices between these teeth may become more 

 or less filled up, resulting in a comparatively smooth edge, and this appears to 

 take place in certain species of such genera as Himerometra and Zygometra. 



In a few species, such as Strotometra omatissima (part 1, figs. 101, 102, 

 p. 163), Perissometra patula, Charitometra basicurva, Eudiocrinus ornatus (fig. 

 190, p. Ill), H eterornetra crenulata, and Heterometra a-spera, the distal border of 

 the earlier wedge-shaped or oblong brachials is abruptly turned outward, form- 

 ing a conspicuous ridge across the arm. This reaches a maximum in Strotometra 

 omatissima and is well illustrated in Charitometra basicurva and in Eudiocrinus 

 ornatus, but in the other species it is only slightly marked. 



In most comatulids the lateral edge of the ossicles is smooth and straight, but 

 occasionally it becomes produced, wholly or in part. Such a production of these 



