84 
“The generic name T rihr achy ocr inns,'' said the late Mr. Telix Ratte/ 
“ was proposed hy Professor M‘Coy on tlie supposition that there were only 
three arms ; hut if, according to Wachsmuth and Springer, the two ancliylosed 
hrachials supported two arms each, more tlian mere rudimentary, then our 
fossil would have had three large and four smaller arms. Tliis being so, the 
name etymologically considered is now a misnomer ; nevertheless it conveys 
to the mind the notion that there were three conspicuous arms.” 
Examples of the type species are usually more or less distorted, 
produeed more towards the posterior side than even the unsymmetrieal 
arrangement of the plates would warrant. Such, however, is not the case in 
T. cornigatus, Ratte. This asymmetry is well expressed by M'Coy, who 
says, “ The cup is not symmetrical in form, like that of other Crinoids, but is, 
as it were, humped on one side.” 
The plates of the calyx have been hitherto described liy M‘Coy, Ee 
Koninek, and Ratte as three in the artieular ring, five in the succeeding 
ring, followed in the next tier by three radials, three interradials, and one or 
two anal plates. To these Ratte has added costals. Messrs. 'Wachsmuth 
and Springer, on the other hand, from an examination of a cast of T. 
corrugatus, supplied to them by the late Mr. Ratte, inferred that the third 
ring of plates “ was composed of seven pieees, of which five were radials, the 
two others azygous plates, but that none of them are interradials. In three of 
the radials, the articulating faces form a straight horizontal line, and only 
these plates are opposed by regular brachials ; the two others, those of the 
two antero-lateral rays being angular and higher at their distal ends.”“ 
After a very careful examination of all the specimens within my reach, I 
must express my entire concurrence with their view, so far, of the calyx 
structure of T. corrugatus, and I am able to state that precisely tlie same 
features are observable in that of T. Clarkei. The cause of the asym- 
metrical posterior side of the last-named species will naturally be inferred 
from the reading of its structure by the light of Wachsmuth and Springer’s 
remarks. The region of the anal plates in the majority of Paloeocrinoids 
seems to be the point of least resistance, and tbe “humped on one side” 
appearance described by M‘Coy is simj)ly caused by the peculiar form of 
the posterior basal, as shown by Ee Koninek,® and the displacement, to a 
' Proc. Linn. Soc. N.S. Wales for 1886 [1887], I ('2), Pt. 4, p. 1075. 
^ Revision of the Palaeocrinoidea, 1886, Pt. Ill (2), p. 250 (174). 
’ Foss. Pal. Nouv.-Galles du Sud, 187L Pt. 3, p. 162. 
