246 NATURAL SCIENCE [April 



First let us see what are the concrete facts that have to be 

 represented in nomenclature. 



The Sub-family Pentacrininae contains crinoids that have a long 

 stem {St), with five angles more or less marked, and with cirri (c) or 

 side-branches springing from the sides in whorls, usually of five. 

 The stem possibly ends in a root in early life ; but it has the power of 

 breaking away just below each whorl of cirri, so that the adult crinoid 

 is to some extent free-moving, and attaches itself by the cirri at the 

 end of its stem. The stem-ossicles or columnals are united by five 

 bundles of ligament, on which they are threaded, as it were, and the 

 articular surfaces are marked by crenelate elevations which surround 

 these bundles, and so assume a petaloid shape ; tlie elevations of one 

 columnal fit into depressions in the next. This stem supports a 

 crown ; and this crown may be divided into (a) a cup containing 

 the viscera, and (5) branching arms. The cup consists essentially of 

 three circlets of five plates alternating with one another, namely : In- 

 frabasals, next the stem; Basals {B); and Eadials {R) supporting the 

 arms. But as a rule the infrabasals are minute or atrophied in the 

 adult, and the basals also are often so reduced in size that the radials 

 rest partly on the top columnal ; while to make up for this the lower 

 ossicles of the arms (the proximal brachials) form part of the sides 

 of the cup, i.e., help to surround and support the viscera. The arms 

 always bear fine branchlets, given off regularly on alternate sides, 

 and known as pinnules {p), and in addition the arms always fork at 

 least once. 



The Sub-family includes at least four genera, which, to avoid 

 controversy, I shall call A, B, C, and D. A begins in the Trias and 

 persists to Eocene time. It has a cylindrical or prismatic stem, and 

 the crenelations on the articular faces of the columnals are confined 

 almost entirely to the circumference, while the five ligament areas are 

 limited by five thin, raised and slightly crenelate lines, which radiate 

 from the centre of the columnal (fig. VIIL). The cup is not well known; 

 the arms fork more than once into equal divisions. B was dominant 

 in Liassic seas, less abundant in Oolitic. The crenelations on the 

 articular faces of the columnals are delicate, and are arranged in five 

 narrow petals quite distinct from one another (fig. IX.). The cirri are 

 often numerous and are laterally compressed so as to have an ellip- 

 tical or rhomboid section (fig. II.). In the cup, infrabasals can usually 

 be distinguished ; the radials are prolonged downwards over the 

 columnals next the cup in spine-like processes (fig. I.) ; they support 

 large arms which branch in such a way that each main division bears 

 Si number of minor armlets all coming off on the same side (fig. I.). 

 C is found in Triassic and Jurassic rocks, but became more promi- 

 nent in Cretaceous times, and is the chief representative of the Sub- 

 iamily at the present day. The crenelations of the columnals are 



