1908] Bohertson. — Incrusting Bryozoa. 277 



polypide passes on emergence from the zooeeium. The chamber 

 in M^hich the polypide is contained is thus vase or bottle-shaped, 

 its proximal portion forming the body of the vase, the narrow 

 distal portion the neck. On each side of the neck, between it and 

 the lateral edges of the zoo'cinm, two foramina, for., are formed. 

 These vary somewhat in size and are covered only by a layer of 

 ectocyst. The anterior rim of the cryptocyst widens so as to 

 unite with the lateral edge of the zooeeium above the foramina, 

 but it fails to unite with the lower or proximal edge of the oper- 

 culum. In this way a large and variously shaped orifice, or., is 

 formed which is divided into two portions by the lower rim of 

 the operculum, the posterior part, p. or., being covered by the 

 chitinous ectocyst, the anterior part, ant. or., by the operculum, 

 op. 



The function of the foramina was first recognized by Jullien 

 ('88), who regards them as places of attachment for certain 

 muscles whose contraction depresses the ectocyst, thus exerting a 

 pressure on the fluid within the zocecium, and bringing about the 

 extension of the polypide. From his study of Steganoporella, 

 Harmer ('02) is in complete agreement with this opinion. No 

 detailed study has been made of the species of TlialamoporeUa 

 common in our southern waters, but examination of cleared and 

 stained preparations of the younger and more transparent parts 

 of a colony, plainly shows through the transparent walls of the 

 lateral foramina a large number of muscle fibers, and there is no 

 reason to doubt that the foramina afford a point of insertion for 

 these muscle fibers. 



48. Thalamoporella rozieri (Audouin) Ilincks. 



PI. 17, figs. 27, 27a, 28, 29; pi. 18, fig. 30. 



Flustra Bozierii Audouin, Sav. 1811, pi. 8, fig. 9. 

 Membranipora Eozieri, Busk, 1854, pt. 2, p. 59, pi. 65, fig. 6. 

 i'Membranipora goihica Busk, 1856, p. 176, pi. 7, figs. 5-7. 

 Steginoporella Eosierii, Smitt, 1873, pt. 2, p. 15, pi. 4, fig. 102. 

 Steganoporella Bozieri, Hincks, 1880a, vol. 6, p. 379, pi. 16, fig. 3. 

 Thalamoporella Bozieri, Hincks, 1887; vol. 19, p. 164. 

 Thalamoporella Bozieri, Waters, 1887, vol. 20, p. 186. 



Zoarium of large size, forming foliaceous expansions, incrust- 

 ing stems and fronds of fucus (pi. 17, fig. 27a), or erect, branch- 



