KONGL. SV. VET. AKADEMIENS HANDLINGAK. BAND 



25. n:o 2. 45 



coiling of the steni. A similar groove, however, appears to run close to the inner median 

 suture; but this is doubtful. 



In the involute portions of the steni the thickness of each ossiele is a little more 

 on the onter curve tlian on tlie inner: thus the steni naturally tends to coil without the 

 lielj) of any special ligaraent on the inner curve, although such may have been present. 

 The uncoiling of the steni is produced by the simple contraction of the large muscles on 

 the outer part of the articular snrface. The different species vary in the extent to which 

 the steni is nornially coiled, and probably in the extent to which it could possibly be 

 coiled: specimens with the crown extended are very rare. 



In all known specimens the left anterior radius of the cup is turned to the outer 

 cnrve of the coiled steni as in fig. -36. 



The attachment of the stem has not been seen in this genus, except in H. scolo- 

 pendra which is referred hcre with some donbt. We learn, however, from a specimen of 

 H. flabellicirrus, tliat, in the distal region, the cirri were long and numerous and more 

 thnn two to the whorl: whether all 5 cirri were evcr present is doubtful. It is very 

 probable that the animals usually broke off any rooted attachment they may have formed, 

 and that they clung to corals or other submarine objects by their cirri. In some speci- 

 mens the stem narrows at the distal end (Pl. II, fig. 52); and this suggests that the crea- 

 turcs may have had some power of loconiotion, such as might have been effected by suc- 

 cessive contractions and extensions of the stem. 



In discriminating »Species of this genus reliance has to be placed entirely on the 

 stem. The crown is too rarely visible; and it nia v bf> doubted whether it would ever 

 yield differentiating characters. Now that the morphology of the genus is understood, it 

 is lcgitimate to found species on the evidence of stems alone. The arrangement of the 

 cirri is the chief diagnostic character; of less importance are the shape of the cirrus- 

 ossicles, the state of the longitudinal sutnres and the extent of coiling; the shape of the 

 stem-ossieles is chiefly dependent on these points and fairly characteristic, 



Four species of this genus have been described from America, H. convolutus, H. 

 brachiatus, H. bridgeportensis and H. Gorbyi. The two latter I find myself unable to 

 recognise, partly owing to the bad preservation of the specimens and partly owing to the 

 perplexing way in which Mr. Miller has chosen to describe them; but the species theni- 

 selvcs may be good ones. Only one species has as vet been described from Europé, H. 

 Fletcheri, of which //. héterocrinus is a synonym. Both Chaklesworth and Salter, how- 

 ever, nientioned the existence of more than one sj)ecies; and it is the case that at least 

 one other species occurs in England, for which is here proposed the name of H. Ammonit. 

 In Gotland both H. Fletcheri and H. Ammonis occur, and there are also found two other 

 species here described under the names of H. flabellicirrus and H. scolopendra as well as 

 one specimen of H. convolutus. To facilitate comparison, a diagnosis of the American 

 species H. brachiatus is here given. The relations between these species are roughly ex- 

 pressed in the accompanying table. H. Fletcheri is the most numerous in individuals 

 and the most widely distributed, and is structurally intermediate between the others. 

 H. brachiatus, H. scolopendra and H. flabellicirrus offer some points of resemblance and 



