220 SMITHSONIAN INSTITUTION 



Sagenocrinus clarki n, sp. 



Plate XIX, figs. 4a-d 



A large species. In general form similar to S. expansus, but differing 

 decisively from it by having a sharp abrupt median ridge following the brachial 

 series from near the radials to the arm bases. Calyx plates seem thinner, arms 

 relatively shorter, and base narrower. Sutures straight in the calyx, not 

 beveled; slightly sinuous in the arms. 



The unique type specimen was found near the close of the collecting in the Niagaran 

 beds near Decaturville, Tennessee ; it is badly crushed, but by patient cleaning I have been 

 able to expose both sides so that all the essential characters may be observed. The best pre- 

 served side is so much distorted that a direct figure of it would give little information, but the 

 form and proportions of the plates can be accurately determined by measurement and by 

 observation from different angles not possible to show in a figure. From these sources a 

 careful restoration has been made from the anal side, which gives the normal contour and 

 proportions of the crown. The radianal is much narrower than the adjoining basals, espe- 

 cially at the lower margin, as may be seen from the restoration and diagram on Plate XIX, 

 figures 4b, d; and it is relatively narrower than I have observed in any specimen of 

 S. expansus. Without changing the relative positions of plates, a little further lateral crowd- 

 ing of the basals would detach this plate from the inf rabasals and put it in substantially the 

 same position as that of S. americanus. 



The general outline of the calyx is more rotund than in most English and Swedish speci- 

 mens, although when compared with a perfectly preserved and undistorted calyx of 5\ expan- 

 sus, such as Plate XVIII, figure 3, the difference in this respect is not striking. The narrow, 

 abruptly raised median ridge along the brachials is a decisive character, of which no trace 

 has been seen in the other species. There is probably also a difference in the less uniformity 

 of the columnals in this species ; parts of the column in several specimens of S. expansus other 

 than those figured show it to be very regular in the alternation of narrow and wider ossicles 

 of very uniform length. In the figure of this specimen may be seen a large number of very 

 small plates scattered promiscuously over the calyx ; it is not certain that they belong to it, 

 but as there was no other crinoid in immediate contact it is probable they do, and if so can 

 only be remnants of the tegmen pushed through between the arm bases by pressure during 

 deposition at the sea bottom. 



The great similarity of many other crinoidal forms of this locality with those of Dudley 

 and of Gotland would lead us to expect a greater resemblance of this species to the European 

 type than to the other American species. 



The specific name is proposed in honor of Mr. Austin Hobart Clark as a slight evidence 

 of my appreciation of his great work on the Recent crinoids. 



Type. Author's collection. 



Horizon and locality. Silurian, Niagaran Group, Brownsport limestone, Beech River 

 formation ; Decaturville, Tennessee. 



