I98 SMITHSONIAN INSTITUTION 



lover of Nature, and a zealous collector until the last, he was in his personal relations and 

 friendships a most lovable man. To his sympathetic kindness I am indebted for a number of 

 unique specimens, which he hoped might be of use to Science in my hands. 



Type. Author's collection. 



Horizon and locality. Lower Carboniferous, Knobstone Group ; Clark County, Indiana. 



Mespilocrinus thiemei n. sp. 



Plate V, figs. 20a, b 



A small species. Crown elongate ovoid, subpentangular ; 9.5 nun. high by 

 7 mm. wide, widest about I Ax; spread of calyx from base to top of RR, 1 to 3; 

 height to width, 1 to 1.5; base rounded. 



IBB small. Post. B very large, rising nearly to level of RR. Height of 



B to R to IBr, 2.7 : 2.2 : 2. Radial facets strongly curved, not filling distal face 



of RR. IBr and higher brachials relatively narrow, height to width about 1.6 



to 2 ; rounded and not in close contact laterally. IIBr mostly 3, with another 



bifurcation visible. RR and Br symmetric, and rays not twisted. Anal x very 



short, not filling interradius, and probably followed by others or by perisome. 



Column small, round; proximal columnals for several joints very short, with 



convex sides, gradually increasing in length so far as preserved. 



The unique specimen upon which this species is founded was in a collection made by 

 Dr. Otto Thieme, one of the pioneer collectors of Burlington, and acquired by me in 1870. 

 It has rested in the tray along with other Mespilocrini ever since, with a strong " ? " upon the 

 label. In all the other contemporary collections of Barris, White, Wachsmuth and myself, 

 and those made in nearly 40 years following, no other specimen of it has appeared. It departs 

 from the typical form of the genus in the fact that the first primibrachs do not fill the full 

 width of the radial, but there is left at each side of the deeply curved radial facet a short 

 shoulder, apparently unoccupied. Hence the rays are not in contact, but small open spaces 

 are left between them. The specimen is very well preserved in a fine-grained matrix easily 

 removed and favorable to the preservation of minute structures ; but I have been unable to 

 detect any trace of small plates in these interbrachial spaces. In this respect it is somewhat 

 in the condition of the aberrant species described under Lecanocrinus, now referred by me to 

 Asaphocrinus ; but the parallel does not continue further, for the anal plate, although quite 

 different from that of the typical species, does not vary in the direction of the tube-like series 

 of the Taxocrinidae. This short and wide plate is decidedly straight above, and was 

 undoubtedly followed by others, but whether solid plates or an integument of small ones, as in 

 Pycnosaccus, cannot be ascertained. The latter is the more probable, because if there had 

 been a solid plate filling the arch of the posterior rays, as in the genus generally, there is no 

 reason why it should have disappeared ; whereas the integument of small plates is a most 

 fragile structure, and in forms like this usually falls to pieces and is lost. If the latter were 

 the case, and as would undoubtedly follow the regular interbrachial spaces were also occupied 

 by small plates, this would constitute a perfectly good genus holding the same relation to 

 Mespilocrinus that Pycnosaccus does to Lecanocrinus, — in other words, the Carboniferous 

 successor of Pycnosaccus. When we remember that in over 50 years' collecting at Burlington 

 only a single specimen was ever found showing the true interbrachial structure of Niptero- 

 crinus, and that it is only now after the lapse of 30 years since Angelin described Pycnosaccus 

 that the actual structure of the same parts in that genus is made known, it need not be thought 

 strange that the same fact as to this extremely rare form should still be open to conjecture. 



