342 



possession of scattered pores and of an occasionally present median avicularium 

 proximally to the aperture. 



Stnittina acaroensis n. sp. 



(PI. XVIII, figs. 12 a-b). 



The zocecia are usually elongated, with an arched or angularly bent distal 

 wall and as a rule with parallel lateral walls. They are provided with a single 

 or double circle of marginal pores, soon separated from one another by ribs 

 which after a time increase in height and length, and in the oldest zocecia the 

 whole surface is divided into a number of depressed areas; the latter may even 

 conceal the chamber of the avicularium. The aperture, the distal margin of which 

 is finely dentated and in the younger zocecia bears the marks of 4 spines, is pro- 

 vided with a somewhat distinctly marked off, broad and deep sinus, the middle 

 part of which is occupied by a fairly broad tooth, axe-like in shape and running 

 out into two pointed corners. The two hinge-teeth are strong, triangular, some- 

 what pointed, more or less strongly striated and curved somewhat proximally. 

 The operculum is membranous, not distinctly separated from the compensation- 

 sac and provided on each side with a very faint chitinous ridge. The peristome 

 is collar-shaped, prominent, and provided with an excision corresponding to the 

 frontal area of the avicularium. Each distal wall is provided with 8 and the dis- 

 tal half of each lateral wall with 3 — 5 uniporous rosette-plates. 



The ooecia, which are present in great number, are large, as a rule some- 

 what elongated, fairly strongly arched and provided midway with numerous, 

 larger and smaller pores. An ocecial cover appears after some time and in older 

 ooecia only leaves a narrow, central part «free. 



Avicularia. An avicularium is present proximally to the aperture, the length 

 of which is almost a fourth of that of the zooecium and which takes up the 

 greater part of the breadth of the zooecium. Its chamber, which is separated from 

 the zooecium by a broad, arched line, is provided at the margin with 3 — 5 pores, 

 and the transverse bar which divides the oval frontal area into two parts, is 

 provided with a short, proximally directed process. The subopercular area, which 

 is turned towards the aperture, has a transversely oval opening. 



The colonies occur as free, two-layered laminae, and the species was found 

 in mud from Akaroa Harbour, New Zealand (Suter); depth 6 fathoms. 



