138 W. A. Parks — Parasite from the Devonian Pocks. 



portion at different points, so that in any one section greatly 

 different appearances will be presented by this part of the 

 skeleton. Vertical sections, however, show that the pillars con- 

 tract in diameter and the elements composing them gradually 

 arch over and unite, so that certain parts of the network are 

 supported on elliptical arches open at the bottom to the fine 

 brown lines separating the pillars at the base. The interpreta- 

 tion is easy, therefore, that each alternate angle of the hexag- 

 onal mesh is supported on a pillar and the alternate angles on 

 a vaulted arch derived from the fused elements of those pillars. 

 Nothing further is revealed by vertical sections, variable as 

 they are, except that the clear matter forming the dividing lines 

 in the pillars expands in the reticulation and ascends almost to 

 the surface of the network, where it is covered by the white 

 matter forming the sides of the meshes. Vertical sections 

 are shown in fig. 6. 



The thickness of the entire encrustation in the hexagonal 

 variety is about three-fourths of a millimeter. The rhomboidal 

 species attains a greater height, possibly as much as two milli- 

 meters. 



The zoological affinities of these parasites is somewhat diffi- 

 cult to determine. The regularly reticulated skeleton at first 

 suggests the Bryozoa, but the peculiar support on the pillars 

 and the structure of the skeletal matter are features that must 

 remove the organism from that association. 



The occurrence of the parasite on shells of gastropods natu- 

 rally leads one to the consideration of Hydractinia, and it is 

 highly probable that our species are closely related to that or- 

 ganism. 



Tangential sections of Hydractinia show a network of chi- 

 tinous fibers with round pillar-like elements at the nodes. The 

 nearer to the base that such sections are prepared the more 

 pronounced are the regularity of the mesh and the individual- 

 ity of the pillars. Higher sections show that the reticulation 

 becomes more and more irregular as we approach the surface. 

 In the short time spent in examining the skeleton of Hydrac- 

 tinia the writer was unable to cut tangential sections low 

 enough to cross the pillars below the first connecting bars, so 

 that a similarity of mode of attachment can not at present be 

 urged in support of the relationship of our species to Hydrac- 

 tinia. 



The two organisms, however, agree in the possession of dis- 

 tinct ascending pillars which give rise to a pronounced reticu- 

 lation by the coalescence of horizontal elements derived from 

 those pillars. A distinct difference is seen in the fact that our 

 species produce but one layer of meshes which has a consider- 

 able vertical extent, whereas Hydractinia repeats this process 



