54 STUDIES IN THE DEVELOPMENT OF CRINOIDS. 



V. FLOROMETRA SERRATISSIMA (A. H. Clark)." 



(Plate XXVII.) 



During a stay at the Biological Station at Nanaimo, British Columbia 

 (on Vancouver Island), in June and July 1915, I succeeded in finding some 

 specimens of Florometra serratissima (A. H. Clark) with Pentacrinoids 

 attached to their cirri. The species was fairly common in a place near 

 Ruxton Passage, in a depth of about 15 to 25 fathoms. It may be worth 

 while mentioning that I observed this species to swim actively in the usual 

 way of Comatulids. Only very few carried Pentacrinoids. In more than 

 200 specimens only 10 Pentacrinoids were found in all, representing the dif- 

 ferent stages figured in plate xxvu. The rearing of the embryos was impos- 

 sible, because the species was not hardy enough to endure the long transport 

 from the place of capture to the station, so that nothing more could be 

 accomplished than collecting the Pentacrinoids. But the study of these 

 alone is of no small interest. 



In the youngest stage represented (plate xxvn, figures 1 and 2) the oral 

 valves have opened, the primary tentacles beginning to protrude. The calyx 

 consists as yet only of the basalia and oralia. The basalia are peculiar in 

 having a rather broad unfenestrated lateral edge; the oralia are deeply con- 

 cave along the middle line, the sides being bent gracefully outwards. There 

 are no infrabasalia. Although the first appearance of the calyx plates could 

 not be observed, the absence of infrabasals appears certain. By dissolving 

 the calyx with dilute hypochlorite of sodium directly under the binocular 

 microscope it is easy to isolate each of its components, and in case the infra- 

 basalia are present they are easily made out; but no trace of them was found, 

 and as it can not well be assumed that they could already have disappeared 

 at least they can not have been absorbed by the centrodorsal, the upper 

 stalk-joints being still quite young, half-moon-shaped it seems safe to 

 conclude that infrabasals are absent in this species. 



While the radialia have not yet been set out, the axillary has already 

 appeared, lying as a small, fenestrate plate about midway on the primary 

 tentacle, outside the first sacculus, which is also distinct. In another spec- 

 imen of the same stage the axillary was only a small spicule, not yet 

 fenestrated. So far as I know, this is the first case recorded where the 

 axillary appears before the radialia. That it is really the axillary which 

 is first formed is shown beyond doubt by the detailed figure (plate xxvu, 

 figure 6), from a slightly older stage where the radial plate has been formed. 

 Here is seen, below the first-formed plate in the tentacle, a small plate which 

 can alone represent the costal. The axillary in this case was found to be 

 slightly abnormal. The anal plate is large and round, encroaching upon the 



34 1 am indebted to Dr. A. H. Clark for the name of this species. 



