928 
MR. P. H. CARPENTER ON A NEW 
(first) radials seem to have been first noticed by ZiTTEL.* For he made them a 
fundamental distinction between the two families of Glyptocrinidce and Rhodocrinidce, 
in which he placed several genera that had been somewhat scattered in previous 
classifications. To the latter he referred types with a more or less depressed or 
spherical calyx, in which the lowest interradials rest directly on the basals, and form, 
together with the radials, a ring of ten alternating plates, e.g., Rhodocrinus and 
Ollacrinus. In the Glyptocrinidce, on the other hand, the calyx is higher, and the 
lowest interradials rest upon the upper edges of contiguous radials. This family 
includes Glyptocrinus and Glyptaster (Hall), with Eucrinus (Angelin), and also 
Thylacocrinus (Oehlert), which seems somewhat out of place ; for it has a large 
globular calyx, and five large interradials, which completely separate the radials from 
one another (Plate 71, fig. 7). 
Messrs. Wachsmuth and Springer! express considerable doubt whether the 
differences between these two families in Zittel’s classification, “ even if they were 
persistent, can be deemed sufficient for a family distinction. Thysanocrinus of the 
Rhodocrinidce has generally at four sides the first interradial disposed between the 
first and second radials; while in Thylacocrinus, according to Oehlert’s figure 
(Plate 71, fig. 7), all five first interradials rest directly upon the basals.” I must 
confess that I cannot quite follow this argument. The Thysanocrinus referred to is 
Hall’s type of that name, which Wachsmuth and Springer subsequently place 
under Dimerocrinus (Phillips) ; and in their generic diagnosis of it they say, 
“ Interradial arese composed of but few plates, the first one large, placed between the 
second radials, and leaning partly against the third, with two small plates above. 
Posterior, or anal area wider, the first plate in line with the first radials, and of the 
same size.” Thylacocrinus, on the other hand, is said to have “Interradials numerous, 
the lower one resting directly on the basals; ” i.e., all five interradials meet the 
basals, and not that on the anal side only. This difference is further recognised by 
Wachsmuth and Springer, for they place the two genera, in different sections of 
their family Rhodocrinidce ; and I do not, therefore, see the force of their doubts 
respecting the persistency of the characters in this portion of Zittel’s classification. 
In fact, they make great use of the position of the lowest interradials in defining their 
subdivisions of the family. 
According to their general description of the Rhodocrinidce, “ In most of the genera 
the first interradial rests directly upon the truncate upper side of the basals, thereby 
separating the first radials all round. In others, however, only the first plate of the 
posterior or anal side is supported by a basal, that of the other four sides being placed 
against the upper corners of the first, and between the second radials, the former 
producing an almost pentahedral, the latter a more or less bilateral symmetry.” This 
* 1 Paleeontologie,’ pp. 374-370. 
t Revision, II., pp. 181, 182. 
