62 THE DEVONIAN OF MISSOURI. 



Tegmen low, convex or flattened; 1/3 to 1/5 the height of the calyx. Ambulacral 

 areas distinct; ambulacrals with regular uniserial arrangement. Primary interambu- 

 lacrals (il amb) 2x5, subequal, elongate, narrow, mirror twins, meeting incorporated 

 pinnulars and occasionally iBr 8 or iBr 4 . illAmb, 1 x 5, narrow, elongate, meeting 

 incorporated pinnulars. Orals (O), if present, 1 slightly modified in form, grouped in 

 front of the anal opening, with the anterior and lateral orals resting against ilAmb and 

 surrounding pO. Anal interambulacrals (An iAmb), 5 or more grouped between the 

 orals, I Amb and il Amb. Anal tube if formed, small. 



Stem unknown; proximal columnals circular, conforming to unexposed outer sur- 

 face of basals; discoidal if the base is flattened, or convex; funnel-shaped if the base is 

 a re-entrant funnel. 



Plate surfaces smooth or ornamented, conforming to the general curvature of the 

 cup or pronouncedly convex. Ornamentation consisting of ridges on the cup plates 

 and papilli on tegmenal plates. Basically the ridges fall into three systems, the neural, 

 transverse, and oblique ridges, which may be laterally duplicated by parallel secondary 

 ridges forming groups of concentric triangles centering at the plate angles. Both pri- 

 mary and secondary ridges may be smooth or rugose, broken up into bars and nodes, 

 suppressed even to extinction or greatly exaggerated. Spines too, altho not discovered, 

 may be found on both cup and tegmenal plates as this type of ornamentation often be- 

 comes spinose. This great diversification of ornamentation and the differences in calyx 

 form furnish the diagnostic characters for specific differentiation. 



All sutures closed; contact surfaces of plates with low relief consisting of minute 

 vermiform ridges. 



Nervous system indicated by 5, unequal, 2 lobed depressions on the visceral side 

 of the basals, and narrow, shallow grooves following the mid-line of the radials and 

 brachials. 



Stereocrinus, derived directly as it was from Dolatocrinus, differs from it in the 

 following characters: In the absence of I Br,, in having but one bifurcation of the arms, 

 at least but one incorporated in the calyx and in the general absence of the free portion 

 of the incorporated pinnules as well as closure of the pinnular neuro-ambulacral canals 

 during ontogenetic development, after the loss of the pinnules. 



Stereocrinus moori n. sp. 

 Plate 6, figures 5 and 6; plate 8, figure 8. 



Calyx of medium size, 1.5 times as wide as high; orally flattened, aborally depressed; 

 aboral depression including BB and RR. IAx convex, curving smoothly from RR to 

 IIBr; 11 Br nearly vertical. Arm bases conical, laterally protuberant. Tegmen flattened, 

 convexity low; depressed interambulacral areas curving smoothly to less depressed 

 ilBrs. Cup ornamented by ridges; three primary and one secondary; neural ridge not 

 accentuated; all ridges rugose: Tegmen papilose. Sutures not incised between ridges. 



Basal 3, forming a deep re-entrant funnel, mostly concealed; exposed rim narrow, 

 rounded. Axial canal quinquelobate, V£ diameter of base. Proximal columnals funnel- 

 shaped. 



Radials and primibrachs subequal in size; IAx higher and narrower than RR. 

 IIBri and IIBr 2 uniserially arranged, those following, smaller, biserial. Arms biserial, 

 pinnulate from IIBri up, bifurcating but once; brachials incorporated to IIBr^ Free 

 portion of incorporated pinnules lost; incorporated pinnular canals closed. 



1 Whether these plates are true orals is not known as a sufficient number of young speci- 

 mens has. not yet been found to satisfactorily trace the ontogenetic development of these 

 plates, but until satisfactory evidence to the contrary is obtained I shall not abandon Wachs- 

 muth and Springers' terminology. 



•The inequality in size of the lobes approaches the trilobed condition but as no calcareous 

 neural capsule was formed the triangularity of the central area is not as well marked as in 

 the Flexibilia and some of the other Camerata. 



