327 



margin, so that the sinus which is rounded at its bottom and narrowed at its be- 

 ginning is bounded by a rounded trapeziform projection, which along its distal 

 margin has a finely serrated hinge-tooth. The operculum, which is well-chitinized 

 and provided with an extremely short and weak muscular ridge within each 

 lateral margin, has two proximal, angularly pointed corners and a proximal, rod- 

 shaped prolongation, which however is somewhat narrower than the sinus. The 

 aperture is surrounded by a low, wall-like peristome, the proximal half of which 

 is very flat. In the ooecium-bearing zooecia the peristome is continued as a fairly 

 high and as a rule flat belt down over the proximal part of the ocecium. There 

 is a well -developed vestibular arch and 6 — 7 spines, which on the ordinai-y zooe- 

 cia form a connected arch, whilst on the ooecium-bearing zooecia three are placed 

 on each side proximally to the ocecium. On an extremely small colony, the place 

 of origin of which is unknown, a somewhat large, projecting tubercle with a flat 

 surface towards the aperture is found immediately proximally to the sinus of the 

 aperture in most of the ooecium-bearing zooecia, but in the single zooecium of 

 the colony without an ocecium there is instead a broad, arched ridge-like pro- 

 jection. This zooecium is possibly not quite normal, as the form of the aperture 

 seems also somewhat different. In the distal half of the zooecium there are ca. 

 10 small pore-chambers. 



The ooecia seem to be endozooecial, the basal half arising within the distal, 

 frontal wall of the zooecium, whereas their frontal half appears distinctly on the 

 surface of the zooecium. They are fairly small and low, without pores and are 

 present on most of the zooecia of the colony. 



Heterozooecia. On each side of the aperture there is a large, somewhat pro- 

 jecting, oval heterozooecium, which may be regarded as a vibraculum ; but the 

 flagellum has an unusual form as it consists of a short, thick, rod part and a 

 lamina running out into three pointed lobes. For the reception of the thick rod 

 part the distal part of the chamber has a bi'oad and deep incision, and the cal- 

 cified transverse bar is plate-like, compressed and widened in a greater or smaller 

 part of the length. It may also be noted that the basal surface of the chamber 

 is continuous with that of the zooecium, for which reason the vibraculum like 

 the pore-chamber can be seen through the basal surface of the zooecium, and the 

 same applies to the vibracula in E. vulgaris, and partly also to those in E. Hynd- 

 manni. Of this species our Museum originally possessed only a small colony with- 

 out indication of locality and the figures on PI. XVIII were drawn from this. 

 Later I have been able to supplement my description from the examination of 

 several small colonies from Siam (Koh Kram; 30 fathoms) taken by Dr. Th. 

 Mortensen. 



