160 FREDERICK W. SARDESON 



in place of the furrows or again at the summit of monticules. 

 The zoarium, if broad, is usually thickest medially, this part 

 then having one, two, or three rows of monticules also. The 

 thicker median part alone appears continued in the stem, which 

 is narrow and thickened to nearly cylindrical form, tapering, 

 ending with a beveled striated articulation area. The articula- 

 tion area and supposedly the basal expansion grew pari pasu with 

 the frond. In old specimens the stalk next to the articulation 

 is solid surfaced, cell apertures having all closed over, except 

 as to the confluent calycals or furrows. 



Interpretation of this form from comparison with those 

 described should include in the first place the suggestion that 

 autocells which are evident are separated by completely subordi- 

 nated mesopores, these being rarely evident, but really always 

 represented in filled condition in the thick amalgamated wall. 

 The confluence of the autocell calycals is explicable as due to 

 the impress of a canal system which was developed strongest 

 in vertical direction during cell increase at the apex; later an 

 all-sided relation between zooids arising, except at the stem, 

 where the basal expansion united. The articulation to the basal 

 expansion shows the zoarium to have been in part non-cal- 

 careous. Again, since no pores or even " tubuli " are present, 

 the closing up of all autocell apertures on the stem argues the 

 cells evacuated by the zooids, except as to the calycals. The 

 general manner of development of calycals argues the same. 



The hemisepta require special mention. They have been 

 said to have "doubtless served as supports for the movable 

 operculum." 1 The said movable operculum is, however, 

 unknown, and the word "doubtless" is unwarrantable. In fact, 

 the hemisepta occur in some species beneath complete tabulae, 

 and in those cases they were isolated from the aperture. In 

 P. subrecta no tabulae intervene, and two interpretations may be 

 admitted for sake of argument. The hemisepta occur one at 

 the bottom and one at the top near the termination of the 

 prostrate or axial cell, their position requiring no explanation 



1 Vide Text-Book of Palaeontology, by C. R. Eastman, Vol. I, p. 279, 1. 4. 



