339 



sides or only on the one side, and a third frequently projects at the same time 

 from the middle of the ooecium. The processes mentioned arise in this way, that 

 some of the above-mentioned rib-like prominences are ring-shaped and continue 

 to increase in height. The ooecium in a larger or smaller part of its circum- 

 ference is connected with the zod'cium by means of rib-like prominences. 



As I have been unable to find any more than a single independent calcareous 

 layer, I conclude that there has been a membranous ectoocccium, by means of 

 which the thickening layer has been formed. The oa>cium lacks a basal mark 

 and has presumably been formed later than the cryptocyst of the zooecium. 



Avicularia. Immediately proximally to the aperture of the zooecium there is 

 a strongly projecting avicularium, standing out at right angles, the chamber of 

 which is almost of the same breadth as the aperture. Seen from the side it is 

 pointed, triangular, and seen from its mandibular surface it has a rounded, tri- 

 angular form. It is provided with an oval aperture but I have been able to find 

 neither a mandible nor trace of transverse bar. 



In the conchological collection of the Zoological Museum a single dry colony 

 was found incrusting Saxidonnis piirpiinttiis from Yokohama. 



The above-described species is only referred with some doubt to the genus 

 Porella. 



Stnittina Norman' (nov. nom.) char, emend. 



Escharella (with subgenera Escharella s. str. and Hserentia) Smitt, 



Smittia Hincks, p. p., Schizoporella Hincks, p. p., Pseudofiustra Bidenkap. 



Spines may be present to a number of 1 — 8. The aperture is provided with 

 a more or less distinctly marked off, as a rule broad, rounded sinus, which 

 sometimes takes up the whole of the proximal margin and the middle part of 

 which is often occupied by a tooth of varying shape. There are well-developed 

 hinge-teeth as a rule. The operculum is in most species membranous or weakly 

 chitinized, often not marked off from the compensation-sac. A peristome may be 

 absent or jjresent in very different degrees of development. Avicularia may appear 

 in verj' varying positions, but one is usually present proximally to the aperture. 

 The ooccia, which in most cases are either independent or have only a small part 

 of their endooa?cial basal wall common with the frontal wall of the zooecium, 

 consist of two calcareous layers, of which the ectoooecium is with few exceptions 

 provided with pores. As a rule there is a more or less developed ocecial cover. 

 The rosette-plates are sometimes uniporous, sometimes with a few or many pores. 



' 84, p. 120. 



22* 



