28 BULLETIN 115, UNITED STATES NATIONAL. MUSEUM. 



With more than 20 arms. 

 Calyx large. 



Base protuberant; tegmen bearing long spines. Arms 



about 30 D. exstans, new species. 



Base shallow concave, Avith small pit, similar to spinosus, 

 but with about 40 arms -D. multibmdiiatus. 



DOLATOCRINUS LACUS Lyon. 



Plate 5, figs. 6, 7. 



Dolalocrimus lacus Lyon, Geol. Surv. Kentucky, vol. 3, 1857, p. 482, pi. 41, figs. 

 2a-e. — Billings, Canad. Org. Rem., Dec. 1, 1858, p. 29, text-figs. 13-18. — Miller 

 and Gurley, Bull. 4, 111. St. Mus., 1894, p. 9. pi. 1, fig. 4. — Wachsmuth 

 and Springer, N. A. Grin. Cam., 1897, p. 311, pi. 261, figs. 6a-c. 



Dolatocrinus approximatus Miller and Gurley, Bull. 4. 1894, p. 25, pi. 3, 

 figs. 4-6. 



This, the type species of the genus, has been thoroughly described 

 and illustrated in the literature. The chief points to observe are its 

 almost rectangular outline in vertical section, the broad and flat 

 base, and relatively high calyx with low tegmen; the ornament is by 

 small central nodes on the lower plates, and a few prominent raised 

 lines, producing distinct stellate figures. The species is rather below 

 medimn size, ranging from 15 to 20 mm. high and 20 to 25 wide. 

 In typical specimens the height to width of calyx is about as 1:1.25, 

 and the width at the flattened base about equal to that at the arms ; 

 but there is variation from this to 1:1.5, the lower forms of greater 

 width having more curvature at the sides and relativeh" narrower 

 base; there is also variation toward fine instead of coarse radiating 

 lines upon the plates. A remarkable enlargement of the base in some 

 specimens beyond anything heretofore known in this group seems to 

 indicate a distinct allied species, D. pyrainidatus . 



Throughout all these variations one constant character prevails, 

 which always arrests attention, and that is that the two or three 

 secundibrachs, with sometimes a biserial pair of arm-ossicles, are 

 incorporated in the calyx in such a way as to produce four conspicu- 

 ous pinnule openings in each interradius, and two, rarely four, in 

 the spaces within the rays; in the latter case they are more crowded. 

 These prominent pinnule sockets, and the broad flat base, give to 

 the crinoids of this type, notwithstanding their small size, a very 

 characteristic aspect. 



Horizon and locality. — This form occurs both at Louisville and in 

 the Onondaga limestone at Columbus, Ohio; and the 30 specimens 

 which I have from the two localities conform closely to the type, sub- 

 ject to the variations mentioned; they show no tendency to modifica- 

 tion in the normal number of 10 arms, the solitary specimen on 

 which Miller and Gurley based their 11 -armed synonym, approxi 

 inatus, being a mere sporadic occurrence. 



I 



