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 som'^, 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 Bourgiieticrimis and Mesocrinus. Rhizocrinus lofotensis and Rhizocrinus 

 rawsoni show these characters very well (PI. IX. fig. 1 ; PI. 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 

 Bourgueticrimis 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 

 obconical, and though it expands gradually upwards it is nowhere very greatly wider than 

 the stem, as is the case in Bourgueticnnus, In Conocrinus suessi and in Conocrinus 

 pyriformis, and perhaps also in Conocrinus seguenzai, it takes on a more ovoid form ; while 

 in Rhizocrinus raivsoni 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 Eiigen. 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 Thiolliericrinus as suggested by de Loriol. The 

 distinguished Swiss palaeontologist 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, pi. v. fig. ]. 

 (ZOOL. CHALL. EXP. PAKT XXill. — 1884.) li 33 



