BY F. RATTE, ENG. ARTS AND MANUF., PARIS. 1159 



The new species which I intend to describe agrees very closely 

 with both Prof, de Koninck and Prof. McCoy's descriptions, 

 but especially with the latter. The specimen is in the Australian 

 Museum. 



The chief difference it presents to Tribrachyocrinus Clarkei, is in 

 the external appearance, the new species being wrinkled or ridged 

 on the surface, whilst the first one is smooth. 



The fossils that Dana has described under the generic name of 

 Pentadia( several species) (1), are probably separate plates of Cyatho- 

 crinus, but they might as well be separate plates of Tribrachy- 

 ocrinus. 



The inner casts of these two genera are often found in the same 

 beds, but in Cyathocrinus the basal plate is formed of five articles, 

 whilst in Tribrachyocrinus it is formed of three articles o:dy as in 

 Platycrinus. 



Calyx. 



In order to afford, besides the diagrams figured, a ready 

 systematic schema of the relative disposition of the plates forming 

 the calyx, I will name these pieces as follows (fig. 1, pi. 68) : — 

 1, 2, 3 for the three basal pieces, A B C D E for the five 

 adjacent subradial plates. 



The anal, inter-radial, and radial plates will be named by 

 composing the letters of the two adjoining plates. For instance, 

 the anal plate being adjacent to A and B, will be called AB, and 

 so on, It will then be easy to read the following tabular 

 disposition : — 



(1.) Am. Jom\ Science. Vol. TV., 1S47, and Geol. U. S. Expl. Exped., 

 p. 713., pi. 4, f. 10. 



