Dec, 1920] Cystids and Blastoids 51 



HOLOCYSTITES CYLINDRICUS GROUP. 



For instance, there is a group of Osgood species, character- 

 ized by their elongate form and by the more or less definite 

 arrangement of their plates, which closely resemble the group 

 of elongate Racine species: Holocystites cylindriciis, H. alter- 

 natus and //. ahnormis. Corresponding to H. cylindricus is H. 

 canneus, with 5 arms, although a few plates are irregularly 

 inserted. Corresponding to H. alternatus are H. hacculus and 

 H. perlongits, each with 5 arms. H. plenus with 5 arms probably 

 also belongs here. Of the less elongate, more ovate species hav- 

 ing supplementary plates inserted very much as in H. alternatus 

 there are //. splendens with 5 arms, and H. faberi, H. parvulus, 

 and H. spangleri with 4 arms. H. ahnormis appears to be repre- 

 sented in its oblique form by H. colletti. After studying these 

 more elongate Osgood forms it seems impossible to avoid the 

 conclusion that we have here a series of species congeneric with 

 the genotype of Holocystites. Unfortunately, the Racine species 

 are known at present chiefly from casts of the interior of the 

 theca, presenting little evidence of the structure of the exterior. 

 The granulose surface of many of these Racine specimens is 

 formed by the fillings of the pores traversing the thecal plates. 

 While these pores appear to be arranged in pairs, no entirely 

 conclusive evidence has been found. No trace of the Omega-like 

 connections between the pores has been noticed. The outlines 

 of the oral and anal apertures are not preserved with sufficient 

 distinctness in the specimens at hand. Finally, insurmountable 

 obstacles result from the entire absence of any knowledge of the 

 food-grooves and of the supports for the arms. This is due to 

 the fact that collectors preserve only the casts of the interior of 

 the theca but make no prolonged search for impressions of the 

 exteriors. The latter usually occur only in large rocks, incon- 

 venient to carry home, and in a fragmentary condition are not 

 readily recognized as of value. 



HOLOCYSTITES WYKOFFI GROUP. 



In contrast to the elongate Osgood species of Holocystites is a 

 group of globose forms, usually supported by a broad, flat base, 

 the flattened area including several of the thecal plates. On one 

 side of the specimen the plates have an elongate hexagonal form 

 and are arranged in more or less transverse rows, while on the 



