laa PAL5:0NT0L0GY OF NEW-YORK. 



edges. On the concave side at the base are two large and strongly arching 

 plates, which extend in long angular points to the lower angles of the 

 concave side ; the angles being occupied by a bent carinate plate, of 

 which the lower narrow extremity reaches to the base of the body. 



On the convex side the base is longer, and formed of three distinct 

 plates, the central one of which is hexagonal and the others apparently 

 pentagonal. On the concave side, the. basal plates are succeeded by a 

 large irregular central plate, and this one by a range of smaller plates ; 

 while the angles present each three plates in direct succession. The 

 convex side above the base shows, somewhat irregularly, five ranges of 

 small plates. The summit is broken off. 



A specimen from the limestone has two round spine-like processes, 

 one from each side of the summit, which, under a lens, appear not to 

 be jointed ; and from the centre is a projection which may be a short 

 proboscis, or the ovarian plates protruded from pressure. These parts, 

 however, are too obscure to be characteristic ; and so far as regards 

 generic relations and differences, we must rely upon the fundamental 

 structure of the body, from the irregularity of which I propose to de- 

 signate this fossil. 



CiE\m Akomalocystites (n.g.). 



[ Gr. avufJuiXi;, irregularis ; xutfTof, vesica.'^ 



Body semielliptical or semiovoid : sides unequal ; the vertical outline 

 oval or ovoid, plano-convex or concavo-convex ; the transverse outline 

 semielliptical, the base of which is straight or more or less concave : 

 the two sides composed of an unequal number of plates. Basal plates 

 three on the convex side, two on the concave side : second series, two 

 large plates at the angles, and fovu- (or five?) on the convex side ; third 

 series, four on the convex side, one at each angle, and a large plate on 

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

 convex side, and a fourth series on the concave side. Base oblique, with 

 the convex side longer, and » deep concavity for the insertion of the 

 column. Pectinated rhombs apparently none. 



