MORPHOLOGICAL PART. ; 71 
Upon commencing the present work, we had an interchange of views 
with Dr. Carpenter as to the best plan to be pursued respecting these plates, 
especially as to whether it would not be better to change their terms, which 
we considered meaningless from a morphological point of view, for others 
more appropriate. We proposed to restrict the term “radials” to the first 
ring of plates of the rays, and apply to the sueceeding ones the terms “ pri- 
mary,” “secondary” and “tertiary brachials,” according to their rank, in 
aul cases, whether the plates were free or not. He replied that he appre- 
ciated the great advantages of the proposed nomenclature, and was willing 
to adopt it in principle; but he thought the terms “ primary,” “secondary,” 
and “ tertiary brachials” were too long and cumbrous, and he proposed in- 
stead of them the terms “ costals,” “ distichals” and “ palmars,” respectively ; 
which we finally agreed to accept. Carpenter announced our agreement 
in a paper “On certain Points in the Anatomical Nomenclature of 
Echinoderms.” * 
In the earlier Inadunata and Articulata, — not in the Camerata so far as 
observed, — the radials are frequently compound, 7. ¢., constructed of two 
segments or parts, which are closely united by a horizontal suture, and in 
the organization of the Crinoid count as one plate.t Among the Fistulata, 
compound radials are found in the Heterocrinide, Anomalocrinidx», Hybocri- 
nidw and Dendrocrinidz. In some of these families they are restricted to 
the right posterior ray, in others they occur also in other rays. We know of 
no case in which the compound structure extends to all five radials, at least 
two of the plates being always simple. Among the Heterocrinids, as a rule, 
the right posterior, and the right and left antero-lateral radials, are compound, 
— exceptionally the anterior one in place of the left antero-lateral; — while 
Anomalocrinus and Ohiocrinus have but two, and Loerinus, Merocrinus, Hybocrinus 
and Hoplocrinus only one. It is further worthy of note, that when there are 
several compound radials, the corresponding parts are of nearly equal size ; 
while the segments vary considerably among themselves in the different 
genera. In LHeterocrinus, Ohiocrinus, Tocrinus, Merocrinus, Hybocrinus and Hybo- 
eystis, the lower portion, —the so-called inferradials, — are considerably 
larger than the upper or superradials. In Anomalocrinus and Dendrocrinus 
the two plates are of nearly equal size; while in Hetenocrinus (Heterocrinus) 
simplex the upper ones are three or four times as large as the lower. In 
* Ann. and Mag. Nat. Hist., Ser. 6, Vol. VI., pp. 11-18. 
+ We gave a full description of these plates in a paper “On the Perisomie Plates,’ Proceed. Acad. Nat. 
Sci. Phila., October, 1890, pp. 378 and 379. 
