REPORT ON THE CRINOIDEA. 257 
“article basal.” It is entirely undeveloped in Rhizocrinus, though this type shows a 
slight decrease in the width of the stem a little below the cup, before the commencement 
of the gradual downward enlargement, just as is so much more marked in Bourgueticrinus. 
There are certain other points in which the two recent species of Rhizocrinus, together 
with some fossil ones, differ very markedly from Bourgueticrinus; and although these 
differences hold good for some of the fossil species of Rhizocrinus, it is difficult to say how 
far this may be the case with others, owing to their imperfect state of preservation. 
In the first place, the basals are of great relative height, often five or six times that 
of the radials, and they occupy much the larger part of the exterior of the calyx; 
while the lower stem-joints are usually longer than wide. If they bear radicular cirri 
these come off somewhat irregularly from near the ends of the joints, but their sockets 
are not verticillate, nor are they ever formed by portions of two apposed joints, as is often 
the case in Bourgueticrinus and Mesocrinus. Rhizocrinus lofotensis and Rhizocrinus 
rawsont show these characters very well (Pl. IX. fig. 1; Pl. X. fig. 15). The latter has 
the longer basals, but its stem-joints, though longer than wide, are not so markedly so as 
in Rhizocrinus lofotensis. The same is the case with the stem-joints of the so-called 
Bourgueticrinus londinensis, which is really a well-defined Rhizocrinus ; while in those of 
Conocrinus (Rhizocrinus) suessi and Conocrinus pyriformis the width of the articular 
faces is more nearly equal to the length of the joint. In all these species the basals are 
longer than the radials, though not greatly so; but in Bourgueticrinus (Rhizocrinus) 
thorenti they are very long, as in the recent Rhizocrinus rawsoni, while the stem-joints 
resemble those of Rhizocrinus lofotensis in their proportions. 
Owing to the shape of the basals, the calyx of Rhizocrinus is usually cylindrical or 
obeonical, and though it expands gradually upwards it is nowhere very greatly wider than 
the stem, as is the case in Bowrgueticrinus. In Conocrinus suessi and in Conocrinus 
pyriformis, and perhaps also in Conocrinus seguenzai, it takes on amore ovoid form ; while 
in Rhizocrinus rawsoni and Rhizocrinus thorenti it may be very considerably elongated. 
So far as I-am aware, no true Rhizocrinus has been obtained from any formation 
lower than the Eocene. Quenstedt' figures some moderately elongated stem-joints of 
Apiocrinus constrictus from the White Chalk of Riigen. But in the absence of a calyx it 
is almost impossible to determine these generically, owing to the rarity of the association 
of calyces and stem-joints at the same spot. The same is the case with regard to the 
Jurassic species of Bourgueticrinus, e.g., Bourgueticrinus ooliticus from the Bradford 
Clay, which is perhaps referable to Thiollericrinus as suggested by de Loriol. The 
distinguished Swiss paleontologist has also described a fossil from the Cretaceous of 
Alabama, U.S., as Bourgueticrinus alabamensis.? It consists only of the basal cone 
which “supports the calyx, and which is composed of several enlarging segments of the 
1 Encriniden, Tab. 104, figs. 64-66. 
2 Description of a New Species of Bourgueticrinus, Journ. Cincinn. Soc. Nat. Hist., vol. v. p. 118, pl. v. fig. 1. 
(ZOOL, CHALL, EXP,—PART XXXII,—1884,) Ti 33 
