159. CONTRIBUTION TO 



Stereocrinus. In fact, the ornamentation of the specimen before us is somewhat 

 like that of Stereocrinus, a genus founded upon a permanently abnormal spec- 

 ies in which each ray has lost its second costal, the shortening and flattening 

 of the body being due to this fact. Other features of Stereocrinus are not 

 wanting in our specimen, small plates above the second interradial being pres- 

 ent in some of the series on the dorsal cup. 



The ornamentation is somewhat like that of D. corporosuSi but stronger, 

 and the radiating lines of nodes fewer in number. The respiratory pores are 

 two to the arm base. The anal tube is central. 



An examination of a large and fine series of Dolatocrinus of quite a number 

 of species from Southern Indiana has forced us to the belief that the number of 

 afms is not always a safe guide in the identification of species. 



The separation of forms, differing little or not at all in shape and ornamen- 

 tation, merely upon the possession or lack of an arm or two is hardly pardona- 

 ble even in hasty work. 



Palaeontologists allow for considerable variation in individuals of species 

 in other orders of fossils and that such variation does exist in outline, ornamen- 

 tation, etc., is well known to every extensive collector. 



Similar results of growth should be expected among crinoids as in brachi- 

 pods or other fossils, but, perhaps, to a less noticeable extent from the peculiar 

 shape of the body. 



If each extra arm base is a sufficient character upon which to establish a 

 species. I believe Mr. Greene has in his possession individuals with from 12 or 

 13 to 20 arms in each group of like ornamentation, omitting the two or more 

 groups of ten armed species. 



The specimen of D. greenei is from the Upper Devonian beds near Charles- 

 town, Ind. 



DOLATOCRINUS MARSHI, Lyon, Rowley. 



Plate 47. Figs. 7, 8. 



There is little doubt of the correct reference of this specimen to Lyon'e 

 species. 



It is a ten-armed form and with a series of six slits between each two arm 

 bases on the vault. The basal plates and the greater part of the first radials 

 occupy a deep inverted frustum of a pentagonal pyramid, the stem having beett 

 comparatively small and with a pentagonal canal. 



Strong carina extend from the base of the frustum near the top of the first 

 radial to the center of the second costal where it forks, sending a low, sharp 

 ridge to each arm base. 



