187 



this yellow marginal part and a lighter, rounded triangular central part. The 

 lateral margins of the operculum are more than usually convergent frontally, 

 and, apart from its proximal concave margin, its form may be described as 

 rounded triangular. The two distinctly marked, well developed adoral areas are 

 furnished with two large acropetal spines, oval or circular in transverse section, 

 which never show any distinct, radiate, but often an annular striation. Of the 

 two opesiulae the larger is of a rather long triangular shape and directed towards 

 the proximal opposite corner. As a rule both opesiular outgrowths reach the basal 

 wall, but with regard to the way in which they meet the latter we may dis- 

 tinguish between two different cases, which judging from the samples examined 

 seem to be about equally frequent, occurring in detached patches at small inter- 

 vals. In one case they meet the basal wall in two separate, open lines, of which 

 one is extremely short, straight or curved, while the other is considerably longer 

 and very hooked. In the other case we have, as in Th. lioticha, a single continu- 

 ous transverse line, but often with an irregular angular bending, in which case 

 the polypide-tube has a low basal wall of its own (fig. 1 f). Transitional stages 

 are however also found between the two cases. The polypide-tube is very asym- 

 metrical and its frontal wall, the proximal part of which is much depressed, is 

 smooth on the greater part of its surface while on the other hand its distal 

 margin is abundantly furnished with tubercles. The cryptocyst is otherwise smooth 

 but has rather large, closely situated pores, which however often do not reach 

 very far. 



Spicules. Only compasses occur, the length of which may vary between 

 0,039 and 0,345'"'" In the smaller of them, found both in the zooecial cavity and 

 between the cryptocyst and the covering membrane, the angle generally varies 

 between 115" and 123", while the largest, found only in the zooecial cavity, are 

 only slightly curved. 



Goecia occur in several places of the examined colony in more or less close 

 groups, partly composed of more or less regular transverse series. Their surface, 

 which shows a more or less distinct concentric striation, is furnished with a 

 greater or smaller number (not exceeding about twenty) of rather large, pyriform 

 pores. The gonozooecia, which may become longer by a half than the ordinary 

 zocecia, have a very large aperture which apart from the sinus makes four-fifths 

 of an ellipse. The operculum of the gonozooecium has a closed, chitinous curved 

 sclerite reaching the distal third of the operculum (fig. 1 e). 



The avicularia, occurring in large numbers and somewhat smaller than the 

 zocecia, have a slightly developed distal, and a more strongly developed proximal 

 cryptocyst, The mandible has as in Th. Rozieri the form of m isosceles triangle 



