

200 



PALAEONTOLOGY OF NEW-YOEK. 



be developed in the same plane with tlie upper portion of these plates, we have the precise 

 form of the costal plates of Lecanocrinus. 



The narrow margin of a plate of the second scries resting on the stem in Ichtiiyocrinus, 

 has its perfect analogy in the intercostal plate of Lecanocrinus. This will be made more ap- 

 parent by inspecting the figure 2, plate 45, which is a representation of the base of Ichtiiyo- 

 crinus, showing the relative position of all the plates to the fourth series somewhat enlarged. 

 By comparing the base of this, or that portion occupied by the summit of the column, with that 

 part of the structure of Lecanocrinus (fig 1 e) inscribed within the circle, the analogy will be 

 seen at once. Beyond the circle are left the five triangular plates of Ichtiiyocrinus, with the 

 intercalated plate occupying a narrow space between them at one point, and succeeded by the 

 other plates as in that genus. 



This analogy is the more interesting, as showing that the tripctaloid pelvis in the crinoids is 

 a higher stage in the development, than the pentapetalous forms, and coincides with the 

 knowledge furnished by geology upon the same point. It has been elsewhere remarked, that 

 in the lower silurian strata, all the true crinoids have five plates in the first series, and it is only 

 in the second period that we have recognized any with three pelvic plates. Thus far we do not 

 know any species with three pelvic plates, so shnple in the organization of its other parts, as are 

 some of those with five plates in the pelvis. By this is meant that no species of this type has 

 been seen, where the brachial or arm-bearing plates continue in direct line from the plates of 

 the second series, and have simple arms and fingers, or fingers composed of a single series of 

 plates placed in direct line one above another. 



Fig. 1 a. An individual preserving a portion of the column. The upper part of the arms being 



crushed, gives it a different appearance from entire specimens. 

 Fig. 1 h. A larger specimen, showing the intercalated plates between the costal and scapular 



series. 

 Fig. 1 c. The opposite side of the same specimen, showing the simple structure. The specimen 



is slighty distorted at the base, showing the point of attachment of the column. 

 Fig. \ d. A. smaller specimen, showing the side with the intercalated plates as in fig. 1 b. 

 Fig. 1 e. The crown of this specimen, showing the infolded arms. 

 Fig. 1 /. The base of the same. 

 Fig. 1 g. The structure of this species, as shown in the preceding figures. The subdivisions of 



the arms are carried out in direct lines over the large scapular plate. 

 Fig. 1 A. A fragment of the column enlarged, with a section of the same size, showing the 



crenulations near the outer margin of the joints, the form of the canal, etc. 



Position and locality. In the shale of the group at Lockport. 



.,*, For description of remaining figures on Plate 45, see end of the article on Crinoidea. 



