16 CALAMOCEINUS DIOMED-E. 



Plate 42, Figs. 1% 2% Plate 53, Fig. 1% Plate 54, Fig. 1% Plate 56, Fig. 2), 

 , there must have been on the inner faces of the first radials of these species 

 of Apiocrinus projections or protuberances similar in their function to the 

 wedge-shaped projections riv, r iv , figured on Plate XX. Fig. 2, for Cala- 

 mocriuus, which were separated by deep grooves extending from the cen- 

 tral part of the radial towards the interradial sutures. 



It is interesting to compare the course of the muscular furrows in the 

 radials of Calamocrinus with the excellent figure given by Beyrich (Crinoi- 

 deen des Muschelkalks, Plate I. Fig. ]'') of their course as seen in the 

 interior of an Encrinus calyx. They are not always curved in Calamo- 

 crinus, as Beyrich considers those of Encrinus to have been, and only 

 sometimes to form free open grooves, as they occur in Calamocrinus, or 

 pass into the thickness of the plates. 



In Calamocrinus, as in Hyocrinus, Plicatocrinus, and Marsupites, only 

 the central part of the distal face of the first radial has an articular facet. 

 Carpenter has called attention to the embryonic character of this structure 

 (Pentacrinoid stage of Comatula) ; it is far more general in the Paljeocri- 

 noids than in later forms, where the facets of the first radials occupy the 

 whole width of the distal face of the radial. 



In the Mesozoic and later Crinoids the articulation between the fir.st and 

 second radials is effected by a pair of muscles and two ligaments. Accord- 

 ing to de Loriol, it is absent in Guettardicrinus, in which the reduced 

 articular facet of Apiocrinus has entirely disappeared. The fossae only make 

 their appearance at a later stage of development. The axial cords at first 

 lie upon their upper surfaces, and are gradually taken more deeply into 

 the substance of the plates ; they lie for some time in open canals. Ac- 

 cording to Carpenter, in many Crinoids the distal faces of the radials remain 

 permanently in the horseshoe condition, with ligaments and muscles but 

 poorly developed. 



According to Carpenter, the dorsal ligamentary pit is enormously ex- 

 panded in Millericrinus and Apiocrinus. The muscular fossae are symmetri- 

 cal in the first and second radials, but in ordinary arm joints bearing 

 pinnules they are asymmetrical. The distal angle of the primary radialij 

 is not cut awa3% as in Guettardicrinus, Uintacrinus, and Apiocrinus Roissy- 

 anus, to receive the lower part of the first interradials ; they are placed 

 in Calamocrinus on the distal edge of the two adjoining radials. 



Carpenter says there seems to have been a trifascial articulation between 



