NO. 1846. OX CERTAIN ELEUTHEROZOIC PELMATOZOA—KIRK. 23 



should not have been a lineal descendant of the earlier Helderbergian 

 form. I have examined a very considerable series of both species 

 and although as a rule the specimens of A. cornutus are in an unsatis- 

 factory state of preservation I feel that this is a safe assumption. 

 Furthermore it may be, as is held by Bather, that disparilis and the 

 forms referred to Placocystis are congeneric. I personally feel that 

 this is not the case, there being sufficient difference in the arrange- 

 ment of the plates to warrant a generic distinction being made. A. 

 cornutus, on the other hand, I feel quite certain is distinct from 

 Ateleocystis. If this be the case and if cornutus and disparilis be 

 congeneric Placocystis must of necessity fall into synonymy with 

 Anomalocystis providing Bather's stand be well taken. 



The following description is taken mainly from A. disparilis of 

 which figures are given on Plate 3, figures 9 to 11. Anomalocystis 

 has an elongate theca highly arched on one side, and flattened- 

 concave on the opposite side. The distal portion of the body is less 

 liighly arched and broader than the proximal. Lying on the flat 

 side, \vithout any appendages, the whole body slants downward 

 toward the distal end. 



It is to be noted that lying in its natural position, the greater 

 portion of the lower side does not come in contact with the surface 

 upon wliich the theca rests. Rather the body rests upon the down- 

 ward produced edges of the theca, which act as runners. In Placo- 

 cystis, Plate 3, figures 1, 2, an interesting variation is to be noted. 

 Here the body is raised above the bottom by means of a central, 

 longitudinal keel, which passes well forward from the base of the 

 theca. There are apparently no lateral produced edges. These 

 runners are of obvious advantage in minimizing the amount of 

 friction to be overcome by the animal in pusliing along over the sea 

 bottom. It is to be noted in the case of Anomalocystis that the lateral 

 keels are most strongly developed in the posterior portion of the 

 theca, and it is largely due to them that the body is given the forward 

 tilt that is so noticeable when a specimen is laid upon a flat surface. 



The anterior (distal) portion of the theca presents structural fea- 

 tures not paralleled in any other group of the Cystidea. The body 

 terminates rather abruptly, and in the face thus formed there is to 

 be found an elongate openmg. This opening is oblong, with the long 

 axis parallel to the flattened base of the theca. The opening is but 

 a trifle less than one-half the breadth of the anterior end, and is 

 approxunately twice as broad as high. It seems possible, as will be 

 subsequently pointed out, that this terminal aperture harbored both 

 the mouth and anal opening. The margin of the theca below the 

 mouth projects somewhat forward, this projection being largely 

 formed by a median plate on the bottom of the theca. This plate 

 is better developed and possibly was of great importance to the 



