314 Transactions. — Zoology. 



The lower layer of the colony also presents numerous 

 tailed larvae in various stages of development. A somewhat 

 early stage is figured in fig. 9, I., close by the ovum (ou.). 

 Fig. 10 shows an older larva in which the number of adhering 

 papillaB is four, three being apparently the usual complement 

 as in fig. 11. Two distinct pigment-spots are present in each 

 case — an anterior, small and rounded ; and an irregularly tri- 

 angular posterior of larger size. These are undoubtedly sense- 

 organs, and probably are eye and auditory organ respec- 

 tively. 



Leptoclinum tuberatum, n. sp. Plate XXVI. 



Several colonies were obtained on both occasions. On the 

 first visit, however, all were distinctly alike ; those got sub- 

 sequently differ much in colour, though, as far as I have been 

 able to examine them at all, they are not otherwise distinct. 



The type form is an incrustiug mass of small thickness, 

 O'Smm. to l-5mm., and of a white colour, slightly more 

 greyish than L. niveum, from which it is readily distinguish- 

 able by its stellate appearance at intervals on the surface. 

 On using a lens these starlike features becoiiie still more pro- 

 nounced, and indicate the position of the zooids, which are 

 arranged in irregular rows. 



The branchial pores are large and stellate, there being six 

 lobes of the test projecting radially into each (fig. 3). Under 

 a high power the apertures are seen to correspond with these 

 lobes, the six rays being however very irregular. No common 

 cloacal apertures were observed. But cloacal canals are very 

 largely developed (fig. 2). 



The spicules vary much in size and in the number of their 

 rays (fig. 4). They are always sharp-pointed. They are most 

 numerous in the true surface-layer, and in the second surface- 

 layer (fig. 1), which cuts the base of the endostyle. They are 

 much more numerous between the zooids than above them in 

 the superficial layer, giving the transverse sections the appear- 

 ance illustrated in fig. 3. 



The test histologically is characterized by its possession of 

 extremely numerous test-cells, these being smaller and more 

 numerous than in either of the preceding species. But in its 

 more general features the present form diverges very greatly 

 from all others of which I possess any account. The extreme 

 superficial layer is thrown up into numerous small papillae 

 (figs. 1 and 2), the spicules being absent, thus leaving a deli- 

 cate transparent membrane over the firmer portion of the 

 colony. Around each zooid the test is very thin, and shows 

 only a few spicules (fig. 1), except at two points right and left, 

 \vhere a projection of the test-matrix is found containing 

 enormous quantities of small spicules (fig. 1, j;//.^). These 



