29 Olsson, Devonian Fossils 3 



in the development of its armlets and which becoming concen- 

 trated in a pair of them resulted in the Trichotocrinns type of 

 arm. This development has been attended by the formation of 

 secondary armlets along these two lateral branches and which 

 bear pinnules. We see then in this genus, a case where some 

 of the pinnules have developed into pinnule bearing armlets. 

 These armlets appear to be biserial although this point is not 

 clear, because of their poor preservation. This evolution as 

 traced above is also brought out when these forms are considered 

 in their relation to geologic time. 



Trichotocrinns. Upper Devonian (Portage form" 1 . 



Melocrinus . Silurian and Devonian. 



Mariacrinus. Silurian and Dower Devonian. 



Melocrinus (Trichotocrinus) harrisi, n. sp. Plate 6, Figs. 1, 2; 



Specimen about medium size. Dorsal cup as high as wide, 

 spreading rapidly. Arms five biserial and developing three biser- 

 ial branches, which give off armlets bearing pinnules. 



Plates slightly tumid and beautifully ornamented with well de- 

 fined ridges, those of the second series of plates passing from one 

 plate to another. From the radials a strong and well defined 

 ridge is carried up along the brachials, interruptedly at each 

 plate, and dividing the dorsal area into five nearly equal fields. 

 Because of the hexagonal shape of the plates, the ridges tend to 

 be in the form of six (6) armed stars, all the arms of which seldom 

 join in the center and never do on the radials, but are well marked 

 on the borders of the plates. Between these ridges are situated 

 small bead-like elevations. Suture line deeply grooved. 



Basals four (4) forming a low cup and projecting beyond the 

 surface of the radials. Radials about as wide as high and hept- 

 agonal in shape, except the anterior one, which is hexagonal and 

 rest squarely upon the basal plate. Costals about as wide as high, 

 decreasing in size upwards and hexagonal in shape, except the 

 second costal which is heptagonal and supports on its inner face 

 the next order of brachial, the distichals. Distichals 2x10, those 

 of the same ray in contact laterally. First two rows of distichals, 

 pentagonal in shape, elevated in the center and with two small 

 bead-like elevation on the adjacent and opposite extremities, the 



