175 



jecting basal lip, the free margin of which is strongly rounded, very often angu- 

 larly curved, the frontal margin being more or less distinctly concave or sinuated. 

 It is on either side connected with the lateral wall of the zooecium by a vertical 

 calcareous lamina. The distal wall, which is composed of a basal, horizontal and 

 a frontal, obliquely ascending part, is on either side provided with a multiporous 

 rosetle-plate, and a similar plate is also found in the distal half of each lateral 

 wall. 



Ooecia wanting. 



The avicularia, scattered in rather large numbers among the zooecia, are a 

 little larger than tJie latter but otherwise of similar form. The strongly developed 

 cryptocyst has in its centre a quadrangularly oval opening with crenulated mar- 

 gins, and in the frontal third of this there is on either side a hinge-tooth. The 

 cryptocyst is most depressed in the distal half of the broad, distally rounded, 

 opercular area, which no doubt corresponds to the mandible. On the proximal 

 side of the opening the cryptocyst is less depressed and surrounded by an indi- 

 stinctly bounded, crenulated, marginal portion. There are a few pores in the 

 proximal part. 



Some colonies of this species occurred on the same specimen of Tridacna sp., 

 on which I found Crateropora falcata. 



. Family Thalamoporellidae n. f. 

 (I^ls. VI, Via, VIb, YIt). 



The zoivcia, which always occur in single form, have pores, free calcareous 

 spicules in the shape of compasses or curves and very often two adoral, acropeta- 

 lous spines, as a rule very short and wide. The membranous or very feebly chi- 

 tinized operculum (or opercular valve) is more or less completely separated from 

 the covering membrane by a single (PI. VI, fig. 6 h, pi. VI a, figs. 3 a, 3 b, 4 c, 

 pi. VI b, fig. 5 b) or double (Pi. VI, fig. 5 a, pi. VI b, fig. 3 a, 6 a) chitinous scle- 

 rite, on each side in connection with the opercular arch. The proximal border 

 of the operculum is generally concave, more rarely straight, and in the first case 

 does not fill up the entire aperture, which in most species is provided with a 

 broad sinus. The two opesiulae are separated from the aperture of the zooecium, 

 and consequently the frontal wall of the polypide-tube is not free. The distal 

 wall, consisting of a basal, more horizontal and a frontal, more ascending part, 

 has within its basal margin a crescentic collection of small, uniporous rosette- 

 plates (rarely replaced by one or two multiporous), while the distal half of each 

 lateral wall has a single (rarely two) multiporous plate. Avicularia occur and 

 large very prominent hyperstomial ocvcia, which arise from the whole periphery 



