REPORT ON THE CRINOIDEA. 223 
has twelve (ten) arms, instead of five, as in Hyocrinus. These arms are composed of 
short, stiff joints in which no syzygial unions occur; while they bear short pinnules, 
ul of which, except the first four, consist merely of one elongated joint. Zittel further 
says,’ “ Aus dem Vorhergesagten geht hervor, dass Hyocrinus in Bezug auf den 
Bau der Arme einen differenzirteren Typus darstellt als Plicatocrinus. Immerhin aber 
stimmen beide Gattungen hinsichtlich ihres Kelchbaues besser mit einander iiberein, als 
mit irgend einer anderen bis jetzt bekannten Crinoideen-Genus und durften darum wohl 
derselben Familie zugetheilt bleiben.” It appears to me, however, that this supposed 
resemblance between Hyocrinus and Plicatocrinus is really very superficial ; and that it 
consists essentially in the condition of the thin and somewhat flattened calyx-plates. 
This is also the case with the radials of Bathycrinus, while the ealyces of young Penta- 
crinide have a very considerable similarity to that of Plicatocrinus. On the other hand, 
and apart from the question of basals, the arms of Plicatocrinus, as discovered and 
described by Zittel himself, are utterly and entirely different from those of Hyocrinus ; 
and although de Loriol says, ‘‘ Les analogies tendrent 4 montrer que les deux genres sont 
de la méme famille,”” he concludes as follows, “il faudra peut-étre établir une famille pour 
chacun de ces genres.” This I propose to do in the case of Hyocrinus, the definition of 
the family Hyocrinide being for the present the same as that given above for the genus. 
While resembling Apiocrinus and also many Paleoerinoids in the nature of the stem- 
joints, Hyocrinus differs in several respects from the other Neocrinoids. In the first 
place the apparent presence of only three basals and the small size of the articular facets 
as compared with the great breadth of the radials, give it a strong resemblance to some 
of the Palzeocrinoids, and more especially to the Platyerinide. Although Hyocrinus 
resembles Platycrinus in having a symmetrical, tripartite base, the position of the dorsal 
axis’ which divides the base symmetrically is not the same in the two genera. If a 
Platycrinus be “ orientirt” with the anal interradius posterior, the dorsal axis runs 
from the right anterior interradius to the left posterior radius; whereas that of 
Hyocrinus (ia the only specimen examined) runs from the left anterior radius to the 
right posterior interradius. But the general form of the calyx, as seen from the side 
(Pl. VI. fig. 3), is very like that of the Carboniferous Dichocrinus intermedius, figured 
by de Koninck.* Its composition, however, is different, as Dichocrinus only has two 
symmetrical basals. 
The persistence of the large oral plates is a noteworthy feature of Hyocrinus, but it 
finds a parallel in the Comatulid genus Thawmatocrinus (Pl. LVL fig. 5), and also to a 
certain extent in PRhizocrinus. 
1 Ueber Plicatocrinus, Sitzwngsb. d. LI. Cl. k. baier. Akad. d. Wiss., 1882, Bd. i. p. 112. 
2 Paléont. Frang., loe. cit., p. 63. 
3 See Beyrich, Ueber die Basis der Crinoidea brachiata, Monatsber. d. hk. preuss. Akad. d. Wiss. Berlin, 1871, 
p- 42. 
* Recherches sur les Crinoides du terrain Carbonifére de la Belgique, Bruxelles, 1854, pl. iv. fig. 9. 
