220 PROCEEDINGS OF THE ACADEMY OF [1881. 



with free arms and free pinnules, the radials in Teleiocrinus and 

 their branches and i)innnles, to a certain height, are laterally con- 

 nected and included within the body walls. 



Strotocrinus bears the same relation to Physetocrinus as Actino- 

 crinus to Teleioc7-inus, Physetocriniis differs from the A. prohos- 

 cidialis form, mainly in having a simple anal opening through 

 the vault, instead of a tube, and the same character separates 

 Strotocrinus from Teleiocrinus. 



In E ucladocriniis of the Platycrinidje, the case is the same as 

 in Steganocrinus. In that genus an indefinite number of radials, 

 apparently intersected by syzygies, are formed into long radial 

 appendages, which give off pinnule-bearing arms from opposite 

 sides. It agrees exactly with Platycrinus in the construction of 

 the body, and both have free lateral appendages, in which the arms 

 originate alternately on opposite sides. The arms of Platycrinus., 

 however, are only given off" close to the body, while those of 

 Eucladocrinus, as in Steganocrinus, are given off continuously 

 and the free rays extend almost to the height of the arms 

 (PI. XYIII, fig. 7). 



Not less interesting is the case of Melocrinus, which we take to 

 be a successor of Mariaci'inus (as amended by us). Both genera 

 make their appearance in the Upper Silurian, but, while the former 

 does not survive later than the Silurian, the latter flourishes in 

 greatest profusion in the Devonian. Mariacrinus, in its simplest 

 form, has but four arms to the ra}^, two of which are given off like 

 pinnules from the body toward the interradial spaces, while the 

 two inner ones stand erect, are parallel and lie close together. In 

 other species of the genus, the inner arms give off from one to 

 three additional arms, always directed to the outer side of the ray. 

 The arms are composed of single joints, which bear pinnules in 

 the usual way. The two median arms of the ray, which in Maria- 

 crinus are placed side b}^ side, are connected in Melocrinus by a 

 suture, and appear as a single arm composed of two series of 

 plates, but the suture between them is straight, and the opposite . 

 plates are scarcely ever alternately arranged. That a coalescence 

 of two arms actually took place here, is best demonstrated by the 

 fact, that in the calyx the two parts are not only separate, but 

 often have interaxillary pieces between them, and that each one 

 has a distinct passage. The compound arms of Melocrinus give 

 off at regular intervals, instead of pinnules, lateral arms, which 



