REPORT ON THE CRINOIDEA,. 223 



has twelve (ten) arms, instead of five, as in Ui/oorinus. These arms are composed of 

 short, stiff joints in which no syzygial unions occur; while they bear short pinnules, 

 all of which, except the first four, consist merely of one elongated joint. Zittel further 

 says,^ " Aus dem Vorhergesagtcn geht hervor, dass Hyocrinns in Bezug auf den 

 Bau der Arme einen differenzirteren Typus darstellt als PUcatocrimis. Immerhin aber 

 stimmen beide Gattungen hinsichtlich ihres Kelchbaues besser mit einander liberein, 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 calyces of young Penta- 

 crinidse 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 h, montrer que les deux genres sont 

 dela meme familie,"^ he concludes as follows, " il faudra peut-etre etablir une familie pour 

 chacun de ces genres." This I propose to do in the case of Hyocrinus, the definition of 

 the family Hyocrinid^e being for the present the same as that given above for the genus. 



While resembling Apiocrinus and also many Palseocrinoids 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 Pateocrinoids, and more especially to the Platycrinidfe. 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 (in 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 intermedivs, 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 Thaumatocrinus (PI. LVL fig. 5), and also to a 

 certain extent in Rhizocrinus. 



1 Ueber Plicatocrinus, Sitzungsb. d. II. CI. k. baier. Akad. d. JViss., 1882, Bd. i. p. 112. 



2 Pal^ont. Frang., loc. cit, p. 63. 



^ See Beyi'icli, Ueber die Basis der Crinoidea bracliiata, Monatsber. d. k. preuss. Akad. d. IViss. Berlin, 1871, 

 p. 42. 



^ Kecherclies sur les Crinoides du terrain Carboniffere de la Belgique, Bruxelles, 1854, pi. iv. fig. 9. 



