36 



Just as the part of the frontal wall of the vestibiiliim, which is connected 

 with the operculum, may he chitinized, this may also he the case with a larger 

 or smaller part of the inner wall of the vestihulum, as e. g. in Euthyris clathrata 

 described by Harmer', in which species this writer has described a vestibular 

 sphincter apparatus, similar to that which Hi neks'- formerly noticed in Eiirysto- 

 melhi hihihiatd. In E. clalhrala^ the somewhat chitinized inner part of the vesti- 

 hulum (irsl bends inwards and downwards into the zod'cium and then again 

 bends forwards and upwards in a semicircular fold, the chitinized part of which 

 (labium) in the closed condition of the vestihulum, (its closely to the above- 

 mentioned opercular arch, which in this way forms an under lip, while the 

 labium forms the upper lip. Also in Euthyris ubiecia according to Harmer's 

 investigations there is a delicate labium. Hincks was the first to find a 

 two-lipped vestihulum in "Lcpraliu" bilabiala, and as I have been able by the 

 great kindness of Professor Whi leaves to examine Hincks' original specimen, 

 I can confirm that the sphincter-ap[)aratus like that in E. clathrata consists of 

 an upper lip (labium), formed by the inner j)ortion of the vestihulum, and an 

 under lip, formed by the opercular arch, which Hincks calls »a semicircular chili- 

 nous rim, as it were soldered to the inner surface of the operculums. I have 

 found a quite similar two-lipped vestihulum in the closely connected species 

 Li'pralia' foraminUjerd, while I have found a vestibular two-lipped Sphincter- 

 apparatus of an essentially diilerent structure in the genus Sleyanoporella. It is 

 placed at the proximal part of the operculum, and consists of two (juite similar 

 semicircular lips slightly chitinized at the free margin, both of which are folds 

 of the vestihulum and have no connection with the opercular arch. From the 

 zooecial aperture's distal rim or anter in quite a number of forms there sj)rings 

 a more or less developed, calcified portion reaching into the zocecium, in most 

 cases in the form of a low, arch-shaped calcareous ridge, which seems to have 

 originated from a partial calcification of the inner or basal portion of the ves- 

 tihulum. Such a structure, which we may call a »\estibular arch«, is found in the 

 family Reteporulae (PI. XXill, figs. 4 a — c), where it is as a rule crenulated, in Macro- 

 pora centralis Mac Gill. (PI. VII, fig. 1 a), in most species of the genus Microporella 

 (PI. XV), and in the genera Escharina (PI. XVIII), Escharella (PI. XVII) and Eschuroides 

 (PI. XVII, figs. 5 b, c). It reaches its highest development in the two last-menlioned 

 genera, and it is shown plainly in a number of figures in Busk's Crag Polyzoa '. 

 The species which shows the highest degree of development of this portion is 

 Escharella iliaphana Mac Gill. (PI. XVII, figs. 1 c, 1 ri), and it is here in llie same 



' 19, p. -HMS: 5 .il p. >S^ ' 7, I'l. VI, ligs. 4. 8; I'l. VII, litJs. 1, ;t etc. 



