CRINOID GENUS SCYPHOCRINUS 33 



Waagen and Jahn only recognized interbrachials sensu str. (interradials) up 

 to the fourth range, of which they describe the succession as being 1-2-3-3 

 usually in the regular areas, and 1-2 (or 3) -4-4 usually in the anal interradius. 

 Beyond that they found the plates to be so small, their sculpture so strong, and 

 their arrangement so irregular, that their contours could not be distinguished 

 (pp. 69-70). They viewed this part, constituting the pavage and the 

 reseau, as a structure sui generis, and they wholly failed to understand its 

 origin or relations. Bather, with his usual clear insight, perceived the probable 

 significance of this structure, and in the review above cited (p. 116) pointed 

 the way to its correct interpretation, although the material at his command did 

 not furnish him the complete solution which is now at hand. 



The superficial aspect of these areas is certainly extremely deceptive, the 

 actual arrangement of the plates being often wholly obscured by the very 

 conspicuous rugose surface growth. This is especially the case with that type 

 which takes the form of transverse bands of strongly elevated plates (for ex- 

 ample, var. schlotheimi W. and J., pi. 44, fig. 1 ; and herein PI. II, fig. 1 ; PI. Ill, 

 fig. 4), which while seeming to pass out from the sides of the arms in regular 

 rows do so in a manner altogether misleading and wholly unlike that of any kind 

 of branches or elements ordinarily connected with arms — curving downward 

 instead of up, and being continuous, like ropes suspended from one arm to 

 another. Nevertheless, the chief component parts of these areas are modified 

 pinnules, which by the upward growth of the calyx have become fixed as a 

 part of its solid wall, and thus have lost their original function. 



The complete structure and relations of these parts are perfectly shown 

 by the natural size figure 1 on Plate IV, drawn with great care by Mr. Chapman 

 chiefly from specimens A, B, C, of Plate I, and from the original of figure 1 

 of Plate V. There is a well-marked transition from the finely costate sculpture 

 in the lower plates, through strongly stelliform plates in the intermediate 

 region (lower IIBr), to the strong, rope-like bands above. In this figure, for 

 better comparison, the plates of the pavement in one-half of an interbrachial 

 and intersecundibrachial area are left in outline, with the interpinnulars dis- 

 tinguished by diagonal hatching; so that the position and relations of the 

 pinnules may be seen at a glance. When the arrangement is once understood 

 it may be readily traced in many specimens ; in some, however, the plates have 

 been so greatly altered by secondary growth that it is very difficult to identify 

 the pinnules. We have carefully traced the pinnules in a number of specimens, 

 and find that their relation as shown by these figures is constant and without 

 exception, save for an occasional abnormal plate. They are well shown in 

 specimens of 5". pybumensis (for example, PI. VII, fig. 2b). 



The extraordinary modification of the surface by which the outward 

 semblance of pinnules is thus effaced is produced simply by the development of 



