LOWER HELDERBERG ROCKS. 131 



The proportions of height, transverse and longitudinal diameters, are, in a single 

 well-preserved specimen, almost precisely as 5, 6 and ■!•, and a smaller specimen 

 scarcely varies from these proportions. The surface is covered with grooves, from the 

 numerous subdivisions of the arms. In some specimens the ossicula are but partially 

 preserved, while in others they are almost entire; but from the silicifled condition 

 of the body, it is not easy to distinguish the ossicula of the arms from the granula- 

 tions of the surface where exaggerated by this silicification. The most important 

 only of the subdivisions are shown in fig. 1, 2 & 3; it being impossible to trace the 

 others satisfactorily. In fig. 4, these ramifications are shown as they exist in that 

 specimen. 



Fig. 1. The left side of the specimen, natural size. 



Fig. 2. The summit, showing the origin and distribution of the arms, the upper pairs of 

 pectinated rhombs, the ovarian and anal orifices, etc. 



Fig. 3. The base of the same specimen, showing the lower pectinated rhomb, the ramifica- 

 tions of the arms, and the cavity for the insertion of the column. 



Fig. 4. Diagram illustrating, as far as traced, the distribution of the arms upon the surface 

 of the specimen figured. 



Fig. 5. An enlargement of one of the pectinated rhombs. 



Geological position and locality. In the limestones of the Lower Helderberg group : 

 Cumberland, Maryland. 



Among the remains of Cystidians from the Lower Helderberg group, 

 is a small one, crushed, presenting on opposite sides a very dissimilar 

 character, and without any evidence of brachial grooves upon the sur- 

 face, or pectinated rhombs. The column is deeply inserted in the base, 

 one side of which is longer than the other. I had designated this fossil 

 as Anomalocystites, without being able, from the specimens then in my 

 possession, to understand fully its structure and relations. More recently 

 I have succeeded in determining the form and agreement of certain parts 

 from a specimen of a different species of the same genus, from the Ori- 

 skany sandstone of Cumberland, Maryland. 



This specimen is somewhat ellijitical on its lateral margins, with a 

 deeply concave base, the summit being imperfect. One side of the spe- 

 cimen is convex, composed of numerous and variously shaped plates ; 

 while the other is distinctly concave, and has on each side a sharp an- 

 gular margin formed by the abrupt bending of the plates along the two 



