NEOCRINOIDEA. 44 1 



very gradually widened out, and the top one is not very greatly larger 

 than those below it. 



Family 7. Bonrgueticri7iidce. — In this family the calyx is very 

 simple, consisting of five basals and five radials. The stem-joints 

 are dice-box-shaped, their faces bearing transverse ridges with fossae 

 at their sides which lodge the interarticular ligaments. The stem 

 is attached below by a branching root or by radicular cirri, and 

 there are five or ten slender arms, the joints of which are united 

 in pairs, with a pinnule on the distal joint of each pair only. The 

 disc bears five oral plates of variable size, and the brachial ambu- 

 lacra have two rows of covering-plates. 



This family differs essentially from the Apiocrinidce in the relatively 

 small size of the calycular cavity and in the more or less dice-box- 

 shaped character of the stem-joints. In the type-genus Bonrgiieti- 

 crimis there is a small pyriform calyx, passing gradually downwards 

 into the thickened upper part of the stem, the top joints of which are 

 much enlarged, while it is fixed below by a root-like prolongation. 

 Bourguetic?'imis is essentially a Cretaceous genus, but has been de- 

 scribed as occurring both in Jurassic and in Tertiary strata, solely, 

 however, on the very uncertain evidence afforded by stem-joints. The 

 family is represented by two living genera. Bathycrinns ranges from 

 1000 to 2400 fathoms in the Atlantic, but is not yet known in the 

 fossil state ; while Rhi 20 crimes, which occurs at smaller depths, ranges 

 back to the Eocene Tertiary. In the former type the basals are small 

 and firmly united, while the radials are long and comparatively free, and 

 there are ten arms. On the other hand, Rhizocrinus has long basals 

 and short, closely united radials, as in Bourgueticrinus ; while there are 

 but five arms, the joints of which are united by " syzygy," only the upper 

 joint of each pair bearing a pinnule. In both genera the upper stem- 

 joints are thin and discoidal, while the ambulacral furrows of the arms 

 and pinnules are protected by delicate calcareous plates. The disc of 

 Rhizocrinus is, further, covered by large " oral " plates, which are much 

 reduced or absent in Bathycrinus. 



Family 8. Pentacrinidce. — This family is defined by Dr P. H. 

 Carpenter as comprising forms in which the calyx is small relatively 

 to the stem and arms, and is " composed of five basals and five 

 radials, with underbasals in one genus. The rays divide from one 

 to eight times. The stem bears verticils of cirri at intervals. Two 

 joints are united by syzygy at each node, to the upper one of which 

 the cirri are articulated. The internodes are traversed by five liga- 

 mentous bundles, which are interradially disposed, and give rise to 

 a more or less petaloid figure on the joint-faces. No root nor 

 radicular cirri." The range of the family is from the Trias to the 

 present day. 



The type-genus of this family is Peiitacrinns itself, which has the 

 geological range of the family. In this well-known genus (fig. 289) the 

 joint-faces of the pentagonal stem are marked by crenated ridges 



