﻿schuchert] siluric and devonic cystidea 205 



Original description. — " Body semielliptical or semiovoid; sides un- 

 equal; the vertical outline oval or ovoid, plano-convex or con- 

 cavo-convex; the transverse outline semielliptical, the base of 

 which is straighl or more or less concave: the two sides com- 

 posed of an unequal number of plates. Basal plates three on the 

 convex [or ventral] side, two | —medial basals] on the concave 

 [or dorsal] side; second series, two large plates at the angles 

 lateral basals], and four (or five?) [anal] on the convex side; 

 third series, four [anals] on the convex side, one at each angle, and 

 a large plate on the concave side; a fourth, fifth, and sixth series of 

 anal plates on the convex side, and a fourth series on the concave 

 side. Base oblique, with the convex side longer, and a deep con- 

 cavity for the insertion of the column. Pectinated rhombs apparently 

 none. Arms unknown. Column deeply inserted into the body, com- 

 posed of large joints above, becoming smaller below." ( See hi;". 21.) 



\o species is here mentioned, hut in Hall's next account of this 

 genus the first species and the one generally accepted as the genotype 

 is A. cornutus Hall. 



To the above generic description should be added the following : 

 On the convex or ventral side of both A. cornutus and A.(?) dis- 

 parilis, between the two lowest plates of the median column, there is 

 always seen a rather small opening. In examples of A. cornutus the 

 calcareous plates are not metamorphosed, but they are usually some- 

 what displaced and one can not be certain that this hole is not acci- 

 dental. In A.(?) disparilis, specimens of which are always pre- 

 served as delicate pseudomorphs, all have a large unmistakable open- 

 ing in the same position. In a crushed example of Placocystitcs for- 

 besianus in the National Museum, there also appears to be an aperture 

 on the ventral side, but here it is one plate higher toward the mouth. 

 In the writer's opinion, this opening must be the anus, but as the evi- 

 dence is not conclusive, the fact can not he stated with certainty. 



Arms 2, free, small, and composed of 2 ranges of alternate, imbri- 

 cating, thin pieces. Ambulacral furrows very wide and deep ; 

 ambulacralia minute, about 5 to each ambulacral piece. Column 

 short, with a great central canal, consisting of numerous, imbricating, 

 very narrow segments, each composed of 2 pieces. The suture lines 

 of the columnals are on the dorsal and ventral sides. 



Anomalocystites has been regarded as the same as Atclcocystitcs 

 Billings and Placocystitcs de Koninck. Atclcocystitcs is from the 

 middle of the American Lower Siluric and is not well known, but 

 appears to he distinct. Placocystitcs, so completely worked out by 

 Woodward in the work above cited, has on the anterior side the same 



