36 



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

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

 or smaller part of the inner wall of the vestibulum, as e. g. in Euthgris clathrata 

 described by Harmer\ in which species this writer has described a vestibular 

 sphincter apparatus, similar to that which Hincks^ formerly noticed in Eurysto- 

 mella bilabiata. In E. clathrata ^ the somewhat chitinized inner part of the vesti- 

 bulum first bends inwards and downwards into the zooecium and then again 

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

 (labium) in the closed condition of the vestibulum, fits 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 obtecta according to Harmer's 

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

 two-lipped vestibulum in ^Lepraliai- bilabiata, and as I have been able by the 

 great kindness of Professor Whiteaves to examine Hincks' original specimen, 

 I can confirm that the sphincter-apparatus like that in E. clathrata consists of 

 an upper lip (labium), formed by the inner portion of the vestibulum, and an 

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

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

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

 uLepraliai- foraminigera, while I have found a vestibular two-lipped sphincter- 

 apparatus of an essentially different structure in the genus Steganoporella.- It is 

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

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

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

 zocecial aperture's distal rim or anter in quite a number of forms there springs 

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

 cases in the form of a low, arch-shape9 calcareous ridge, which seems to have 

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

 tibulum. Such a structui-e, which we may call a ^vestibular arch«, is found in the 

 family Reteporidae (PI. XXIII, 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 Escharoides 

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

 genera, and it is shown plainly in a number of figures in Busk's CragPolyzoa^ 

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

 Escharella diaphana Mac Gill. (PI. XVII, figs. 1 c, 1 d), and it is here in the same 



' 19, p. 266; ' 34 p. 23; ' 7, PI. VI, figs. 4, 8; PI. VII, figs. 1, 3 etc. 



