MORPHOLOGICAL PART. 97 
According to Neumayr, the disk of Cyathocrinus is composed of five large 
plates, which, like the Schettelplatten of Haplocrinus, abut against the radials. 
The plates, he thinks, are in sutural contact laterally, but leave at the sum- 
mit a large space for the mouth. The ambulacra are exposed upon the sur- 
face, resting within the deep grooves, formed along the lateral margins of the 
plates. They extend from the mouth to the bases of the arms, and are cov- 
ered by small plates, which project inward over the peristome, and close the 
mouth externally. The small marginal plates, which, as he states, in some 
species extend over the whole disk, he takes to be “ eine secundiire Wuche- 
rung” of the side and covering pieces. 
His description does not agree with our idea of Cyathocrinus ; it comes 
closer to the structure of Huspirocrinus spiralis, from which it was probably 
made, The latter really seems to have but one set of large plates upon 
the disk, which touch the radials, and enclose at the summit moderately 
small plates, which may be ambulacral pieces ; but the former are not orals. 
Cyathocrinus Gilesi, as represented in our figures, has also but one ring; but 
there is a large vacant space at the middle, which was evidently closed in 
more perfect specimens by an inner ring of plates, as in the other species. 
C. brevisaceulus has an outer ring of plates and an inner one, and the ambu- 
lacra, which are exposed upon the former, are hidden by the latter. In C. 
multibrachiatus the outer ring is covered by marginal plates, the inner rep- 
resented by a few irregular, large pieces, scattered upon the surface, and 
intermingled with ambulacral pieces. This specimen was illustrated by 
Neumayr on page 473, from our figure in Part III of the Revision, and he 
must have taken the irregular inner pieces for the orals, for only in this 
way can we understand the explanatory remarks accompanying the figure. 
He says: “ Wachsmuth and Springer figure a most remarkable example of 
Cyathocrinus multibrachiatus, in which, as they show, the orals (summit plates) 
are in process of resorption, and in part replaced by small plates.” In 
C. alutaceus also, he took the inner plates, which in this species are un- 
usually large and regular, for the orals, and for the homologues of the 
outer plates of C. malvaceus,* C. Gilesi, and C. brevisacculus. 
* Neumayr gave (Stamme des Thierreiches, p. 450), after Meck and Worthen, two figures of the ven- 
tral surface of this species: Fig. 2, representing the ‘ Kelehdecke”; Fig. 3, “Dieselbe, nach Entfernung 
der Deckplattchen.” The formerhas five large interradial plates, with a vacant space in the centre, much 
larger than that of C. Gilesi, and the ambulacral grooves are exposed. In the latter the centre is closed by 
seven plates, almost as large, and as regular in their arrangement (a central plate surrounded by six proxi- 
mals), as in C. alutaceus. That he took these plates, contrary to those of C alutaceus, for covering pieces, 
extensions from the ambulacra, and not for orals and central plate, is clearly indicated by the explanation of 
the figures, 
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