A MONOGRAPH OF THE EXISTING CRINOIDS 265 



probable that we may find it in some stalked crinoid. He said that in the comatulids 

 he would expect the case to be the same as in the dendrochirote holothurians, all having 

 a simple larva provided with ciliated rings, but not otherwise specially adapted to a 

 pelagic life. He remarked that the character of the egg boars a relation to this. In 

 all the numerous dendrochirotes he has examined the eggs are large and yolk laden, 

 and he had no doubt that the larvae in these, and probably all other dendrochirotes, 

 will prove to be of the usual simple cucumarian type. In all the crinoids he examined 

 the eggs are likewise rather large and rich m yolk, and he said that he must infer from 

 this fact that their larval form will also bo of the usual simple type. He recalled that 

 I stated that in the Thalassometridae the eggs are small, and accordingly I presumed 

 that they have a long free-swimming stage, addmg that it would be of considerable 

 interest to study the development of some species of this group, for if the eggs are 

 really noticeably smaller in the Thalassometridae than they are in other crinoids, and 

 especially if they are less supplied with j'olk, we may expect their development to 

 afford features of unusual interest. He said that he did not have a sufficient repre- 

 sentation of the family Thalassometridae at his disposal for investigating the character 

 of their eggs; only in Parametra crion he found the eggs to be a httle smaller than those 

 of Tropiomefra carinata — 0.15 mm. in diameter as compared with 0.2 mm. in the latter. 

 Regarding Tropiometra carinata he found that the larvae are not plutei or anything 

 like that. Still there is something in the development to account for the wide distribu- 

 tion of the species. Fii-st the egg is free, probably pelagic, and second the larvae, 

 which are very active swimmers — in the jars they were generally found swimming at 

 the surface — may keep up their pelagic existence for quite a long while. If they find a 

 suitable place for fixation they may attach themselves when only two or tlireo days 

 old, otherwise they may swim for six or seven days, and he had one individual that 

 did not attach itself until it was eight days old. He remarked that as a result of this 

 facultative prolonged swimming period the larvae may be carried for considerable 

 distances by currents, and this accounts in a natural way for the wide distribution of 

 the species. 



KEY TO THE SPECIES AND SUBSPECIES IN THE GENUS TROPIOMETR.\ 



o'. Arms evenly convex dorsally with no trace of a median carination or of median tubercles on the 



distal ends of the brachials; size large, the arms usually about 200 mm. long, sometimes much 



longer. 



6'. Slender, the arms narrow and strongly rounded dorsally, the brachials beyond the base of the 



arm triangular or wedge-shaped, from half again to twice as broad as the longer side (Gulf of 



Aden; 73-220 meters) magniflca (p. 266) 



5". Stout, the arms broad and more gently rounded dorsally, the brachials beyond the base of the 

 arm very short, discoidal or broadly oblong (from between Fremantle and Geraldton, 

 Western Australia, and from Bowen, Queensland, northward to Miudoro, Philippine Islands; 

 from Hong Kong northward to the Korean Straits and eastward to Sagami Bay and the 



Benin Islands; 0-110 1?146] motcns) afra (p. 268) 



c'. Cirri with 21-35 ("averaging 29) segments, 25-40 (averaging 35) mm. long (Mindoro, Philip- 

 pines, and southward to Bowen, Queensland, and to between Fremantle and Geraldton, 



Western AustraUa; O-UO [7146] meters) afra afra (p. 268) 



c2. Cirri somewhat longer and stouter, with 27-43 (usually about 35) segments, 30-50 (usually 

 about 40) mm. long; a more robust and rugged form than the preceding (from Hong Kong 

 northward to the Korean Straits and eastward to Sagami Bay, Japan, and the Bonm 



Islands; 0-66 [?91] meters) - afra macrodiscua (p. 272) 



724008 — 47 18 



