of tilt Crinoidea brachiata. 



403 



remain possible, only one of which occurs. In the pentagon 

 of the inferior basal circle, Avhich has the opposite position, 

 the sutures of the possible divisions acquire the directions of 

 those which w6i-e impossible in the superior pentagon ; and it 

 will be seen from the annexed 

 figure that the mode of divi- 

 sion observed in Taxocnnus or 

 Forhesiocrinus is the only one 

 that was possible if the dorsal 

 axis of the dicyclic tripartite 

 base was to preserve the same 

 position that it possesses in 

 the monocyclic base of Platy- 

 crinus. 



In the figure, the two penta- 

 gons of the monocyclic and di- 

 cyclic base divided in accord- 

 ance with the same dorsal axis 

 are placed one withifi the other, 



the latter, with the sutures belonging to it, being distin- 

 guished by dotted lines. 



From the two first mentioned genera of the Taxocrinidse 

 Ichthyocrinus is distinguished by the fact that the radii, which 

 consist of flat broad segments, may become firmly interlocked 

 in a state of rest. As early as the year 1839, Phillips, Avhen 

 comparing the Cyathocrinus pyriformis of the ' Silurian Sys- 

 tem,' which belongs to Ichthyocrinus^ with Taxocrinus tnher- 

 culatus, remarked that the two Crinoids presented great ana- 

 logies, and that the former might probably form a new genus; 

 his judgment was confirmed by Hall, who ascertained the 

 presence of the dicyclic tripartite base in the American Ich- 

 thyocrinus kevis. According to the diagram which this author 

 has given in the ' Paleontology of New York ' (vol. ii. pi. 45. 

 fig. 2), the polar interradius would be recognizable also in 

 Ichthyocrinus by a small high-placed interradial segment, and 

 the division of the inferior basal circle would correspond with 

 that of Taxocrinus. 



De Koninck's genus Mesjniocrinus is not, as L. Schultze 

 judged, identical with Lecanocrinus. It is distinguished from 

 Ichthyocrinus only by a larger and more developed calycine 

 floor, in which the dicyclic base in combination with the first 

 radial segments has acquired the form of a patina. Of the 

 two species of the genus, the Berlin collection has received 

 from M. de Koninck a patina of Mespilocrinus Forbesianus, 

 the division of which is clearly like that of Taxocrinus^ as is 



