132 



lloating apparatus, as appears to be the case in the Crinoids Tropiometrn 

 niriiKiht and Anicdon pctdsus.^) 



I'jniiK'nlly ( liariKlcrislic of lliis larva is liu' jjody sl<eleton. The body 

 rods are simple, nearly hori/onlally directed; there is a deep sinualion at 

 I he i)()int ol' issue ol' the rods of the aims. Tiu' end rods and the transverse 

 rods ;iic \(i \ slioi I ;ui(l hroad, forming together, as it were, a link between 

 the two parts of the skeleton. — The stage figured is too young to show 

 the shape of the fully formed larva; it is only evident that the postero- 

 lateral arms are fairly broad. By means of the skeletal characters it is, 

 however, possible with certainty to recognize some of the larvae in my 

 material as belonging to the genus Ophiocuma, and through these it is 

 again proved that the larva described in my l^chinodermen-Larven d. 

 Plankton-lixped. (Taf. Vll, Fig. 2) under the name of Ophioplulem Henseni 

 is the larva of Ophioroma which is, accordingly, peculiar through having 

 a kind of epaulets or rather vibratile lobes, otherwise unknown in Ojjhiurid- 

 larva', excepting only the larva of Ophiuvomimi niyia. 



The type specimen of OphiopUileus Henseni had the skeleton dissolved. 

 There is thus no possibility of ascertaining whether the latter is the fully 

 developed larva of Ophiocoma echinata; I would rather be inclined to think 

 that it coidd not be that s[)ecies, the shape of the young larva difl'ering 

 not inconsiderably from the 0. Henseni; especially the hind etlge of the 

 body is so dilTerent that it could hardly depend on age (or preservation) 

 alone. In conlorniity with the nomenclature adopted in this work, 1 shall 

 then designate the Ophiopluleus Henseni as OphiopUileus of Ophiocoma, 

 species a, referring lo the description and figure given in the work quoted. 



Species b. The shape of the body ap])ears lo agree very completely 

 with that of species a; none of the specimens in hand are, however, suf- 

 ficiently well preserved for being figured. The skeleton (Fig. 58) differs 

 from I lull of the 0. echinata-l-drwa in the body rods being quite horizontal; 

 also the basal part of the posterolateral rods is horizontal, the result being 

 an extraordinary width of the skeleton, corresponding to the width of Ihe 

 posterior pari of the larval body, as seen in Ihe figure of species a {Ophio- 

 pluleus Henseni). The transverse rods are very short, pipe-shaped, thick- 

 ened; the end rods are even shorter, also somewhat widened. All the rods 



') Til. Mortensen. Studies in the clevelopnienl ol Crinoids. Papers from tlie Depart- 

 ment of Marine Biology. (Carnegie Inst. Washington. \'ol. \VI. 1020. 



Th. Mortensen. Notes on the developnicnl and Ihe larval I'orins of some Seandinavian 

 Kchinodenns. Vid. Medd. Oansk Naturh. I-'oren. 71. 1020. p. l.'il. 



Also the eggs of Opiiioderma breuispina Say lloal, hut in this case it is liie large loiilenl 

 of yolk which makes them lloat, no special structure of the egg membrane apparently serving 

 as a floating apparatus, ((^asw. Cirave. Ojjhiura hrcvispina. Mem. Biol. I, ah. .lohns Hop- 

 kins Univ. IV. ,'). 1900. — Ophiura brevispina. II. Journ. of Morphology. 27. 1016). 



