26 PR0CEEDIN08 OF THE NATIONAL MUSEUM. vol.41. 



bottom, this forward movement would result simply in sliding the 

 animal along the bottom instead of burying it. While in motion it 

 is probable that the flap, which has been described above, was pulled 

 down. This covered the anterior opening and prevented the intru- 

 sion of undesirable matter. 



The feeding habits of Anomalocystis, as indicated by the structure 

 of the animal, seem to be peculiar to itself and the associated forms 

 referred to the subgroup, at least among the Pelmatozoa. Lacking 

 food-gathering appendages, it is obvious that food must have entered 

 the mouth directly. It seems highly probable that when feeding, 

 the terminal aperture was kept open and the animal without elevating 

 the adoral portion of the theca pushed itself along the bottom. By 

 this process the cystid could fill itself with bottom ooze, in which 

 its food was contained. 



TrocJiocystis. — Trochocystis, which may be considered the most 

 simple known type and perhaps constitutes the radicle from which 

 sprung the remaining genera of the group, is a Cambrian genus 

 described by Barrande. The various interpretations of the genus 

 given by Jaekel (1901), Haeckel (1896), and Bather (1900), are so 

 diverse that one with no more evidence than is afforded by figures 

 alone feels a considerable degree of hesitancy in coming to any definite 

 conclusions regarding the form. This is unfortunate, for upon the 

 correct interpretation of this genus depends to a great extent one's 

 ability fully to comprehend the origin of certain structures to be 

 found in the later tj^es. The uncertainty relative to the structure 

 of TrocJiocystis is to a great part due to the preservation of the 

 specimens, which occur largely as molds, and as such they have been 

 figured. The difficulties attendant upon the elucidation of such 

 material are very great, and are almost insuperable when one has 

 but figures to deal with. 



In Trochocystis we find the theca flattened, indicating the assump- 

 tion and probably fairly long maintenance of a prostrate existence. 

 The two surfaces of the theca are composed of a great number of 

 polygonal plates which are surrounded by 12 comparatively massive 

 marginal plates. A dorsal and ventral surface may apparently be 

 distinguished, both through the relative number of plates comprising 

 the two sides and by the relative extent to which the marginals take 

 part in the structure of the two areas. AboraUy the marginals pass 

 insensibly into the column, which is composed of a double alternating 

 series of plates. (PL 3, fig. 5.) 



It is probable that the stem in TrocJiocystis was far less specialized 

 in function than the equivalent organ in later forms. Owing to its 

 structure, considerable freedom of lateral movement was made 

 possible, but even this is due to the flexibility of the column itself. 

 There was but little or no play at the junction of the column with 



