BATOCRINID^. 511 



Agarieocrinus brevis (Hall). 

 Plate XXXVIII. Figs. 2a-e. 



1858. Acthocritius hrevis — Hall; Geol. Eep. Iowa, Vol. I., Part II., p. 567, Plate 10, Figs, ia, b. 

 1881. Agarieocrinus hrevis — W. aud Sp.; Eevisiou Palfeocr., Part II., p. 112. 



Sjn. Actinoerinus cornicultts — Hall, 1858, Geol. Eep. Iowa, Vol. I., Part II., p. 566, Plate 10, 

 Figs, la, b, c. 



A small and delicate species. Calyx wider than high ; dorsal cup and 

 tegmen of the same height. The lower part of the dorsal cup to the top of 

 the radials slightly concave, thence spreading rather abruptly to the arm 

 bases ; the interradial spaces slightly depressed and somewhat contracted at 

 the arm regions. All plates below the arm regions thickened, and rising 

 above the suture lines in nodose or tuberculous extensions, with short, incon- 

 spicuous ridges reaching to the sides of the plates, where they meet with 

 the ridges from adjoining plates. 



Basals small, forming the bottom of the column depression. Radials 

 a little longer than wide, their ridges occupying only the upper end of the 

 plates, tlie convex lower part being perfectly smooth. First costals small, 

 quadrangular, the sides convex; the second pentangular, shorter than the 

 first but wider. Distichals 2X2, very short, supporting the arms. Arm 

 facets large, subcircular; the ambulacral openings larger than usual in this 

 genus. Arms ten, heavy, slightly increasing in thickness to half their height, 

 then tapering gradually, and ending in a sharp point. First interbrachials 

 large, nearly as wide as long, rising to the top of the first distichals ; the two 

 plates of the second row very narrow, three times as long as wide. First 

 anal plate a little narrower than the radials; the three plates above, which 

 are almost as large as the corresponding single plate of the four regular 

 sides, are followed by four or five small pieces, and these by numerous rows 

 of still smaller ones, which form a ridge, with a well defined groove at the 

 sides. Ventral disk comparatively short, hemispherical, with a large plate 

 in the centre. This plate, which represents the posterior oral, and is almost 

 as large as three of the other oraLs, is surrounded by eight slightlj' convex 

 plates, four of them orals, two overlying the posterior ambulacra, and two 

 the anal side. The radial dome plates, which are so prominent in other 

 species, either are unrepresented, or cannot be distinguished from the inter- 

 ambulacral pieces, which are of moderate size, and only sufficiently tumid to 

 bring out distinctly the suture lines. Anus directed laterally, located half 

 way between the arm openings and the summit of the posterior oral. 



