THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES. 13 



shallow calyx, with a low tegmen composed of innumerable slightly 

 tumid plates, resembling that of the Actinocrinoid genus, Strotocrinus. 



The surface is marked by a most profuse and highly sculptured 

 ornamentation, usually in the form of numerous intricate radiating 

 ridges and furrows passing from plate to plate from the radials up 

 which are sometimes broken up into pits less ornately arranged. 

 The higher brachials leading to the free arms are marked by a con- 

 spicuous longitudinal ridge, with strong lateral processes. There is 

 considerable variety in these surface characters, but they are too 

 much influenced by conditions of preservation to be available for 

 defining species. 



The two special characters upon which the genus is founded are 

 the primibrachs, and the enormous brachial extension of the calyx. 

 These are thoroughly shown by the generic diagram (text fig. 5). 

 While the primibrachs have the normal number of two, instead of a 

 single axillary plate as in Hadrocrinus, they tend to assume an 

 unusual condition, which is the reverse of what is seen in Coman- 

 thocrinus. One of the primibrachs is frequently much modified, 

 but instead of the first, as in that genus, it is here the second, or 

 axillary, plate that is unstable. In about half of the specimens it 

 is more or less reduced in size, and singularly changed in shape and 

 ])ro])ortions, while in others it is of normal size and form all around. 

 In some cases both forms are present in the same specimen. Lyon 

 interpreted the structure of the IBr as being the same as in H. discus. 

 In the intricate sculpture on many of the specimens the sutures are 

 difficult to see, and his type being of that character he did not 

 observe the presence of the two })lates, which are evident in upward 

 of 20 specimens. The modification in form of the axillary is seen 

 in the diagram, which is made chiefly from an extraordinary speci- 

 men obtained since Lyon's time, having the calyx nearly intact, 

 with a spread of about 15 cm., and the surface characters well pre- 

 served from the basal pit to the arm bases. It is finely shown by 

 figure 1 on plate 3. 



The irregularity in the axillary is reduplicated to some extent in 

 the succeeding divisions, which are repeated to the number of 3 to 5, 

 exceptionally 6, at intervals of two plates for the first three bifurca- 

 tions, and longer higher up. After the third axillary the outer ramus 

 of the ray and of the half dichotom remains single, while the inner 

 ramus of the half dichotom branches, so that the number of arms 

 is normally 16 or 17 to the ray, thus making 80 or more arms in 

 all. The final brachial series bears a strong median ridge, and passes 

 into a relatively small biserial arm. The ridges and arm openings 

 are well shown in Lyon's figures h 2, and h 3, and I now have a spec- 

 imen with the arms preserved for a considerable distance (pi. 4, fig. 1), 

 Avhich in their number and small size are in marked contrast to 



