22 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.41. 



There is a general unity of structure among these forms that 

 strongly argues for a monophyletic origin of the group. In all, the 

 theca is flattened on one side and more or less highly arched on 

 the other. The theca is elongate and comparatively narrow. The 

 stem is large in the proximal portion and tapers rapidly distad. It 

 is short and composed of a double row of curiously imbricating 

 ossicles Plate 3, figures 1, 5, 6 — a feature which gives the column 

 great flexibility. The brachioles when present are two in number 

 and comparatively slender, reminding one strongly of the jointed 

 appendages of the Crustacea. No pore-rhombs are present. A more 

 detailed description of the structural features which characterize the 

 group will be found under the discussion of the different genera. 



In the discussion of this subgroup a somewhat unusual treatment 

 will be accorded the forms. Owing to the remarkable modifications 

 exhibited by the members of the group and the evidence of their 

 having lived quite differently from the majority of the cystids, it has 

 been thought best to treat of the best laiown and more specialized 

 forms first. Anomalocystis as representing the terminal member of 

 a highly specialized fine, necessarily possesses the most striking 

 adaptations to the form of life which had been assumed by the group 

 as a whole. For this reason it is possible to predicate with a fair 

 degree of certainty the habits of the animal. Whatever type of life 

 obtained in the case of Anomalocystis we may be fairly sure was 

 possessed to a certain degree by the other forms referred to the group. 

 Furthermore, by taking the most complex form first, we may note 

 its modifications and trace more or less perfectly the steps by winch 

 they were brought about. 



Anomalocystis. — The genus Anomalocystis was founded by Hall 

 (1859, p. 132) with the Helderbergian cystid A. cornutus as genotype. 

 In the same volume he refers another species disparilis, from the 

 Oriskany, to the genus. As a matter of fact the generic description 

 as given by Hall is based upon both species. Bather in Lankaster, 

 refers cornutus doubtfully to Ateleocystis, Billings, and disparilis to 

 Placocystis. Were Anomalocystis and Ateleocystis proved to be the 

 same, it is doubtful winch name should hold. According to the date 

 of publication, it seems that Ateleocystis had precedence. Billings 

 himself, however, in describing the genus (1858, p. 72) says: ''Should 

 it be ascertained hereafter that the two genera are identical, this 

 species must be referred to Anomalocystis, which has the precedence." 

 In this case. Hall had sent out advance sheets containing a description 

 of the genus, wliich antedated Billings's publication. If these advance 

 sheets are to be recognized, the date of Anomalocystis must be shifted 

 back a year or more. 



It may be held, I think, that A. cornutus and A. disparilis are 

 congeneric. Indeed there is no good reason why the later type 



