2I 8 PORIFERA. II. 



It is a surprising fact that in this species only one form of megasclera is found, composing 

 both the dermal and the main skeleton. The question, it is to be remembered, is not of the skeletal 

 spicules having become equi-ended and of the same size as the dermal spicules, but it is a real fact 

 that only one kind is found. According to both form and development it is evident that the mega- 

 sclera here correspond to the dermal spicules in the preceding species, and thus the skeletal spicules 

 have disappeared. It would be interesting to examine embryos of the present species, for, the skeletal 

 spicules being generally the megascleres occurring as the first in the embryos of the Myxillinae, they 

 might possibly be found to be represented in the embryos of the species. 



b. Microsclera ; these are of three forms , sphaerancora; and ancorae spatuliferae of two sizes 

 i. The sphaer ancorae are of the same construction as in AI. clliptica, but they have a peculiar form 

 that may best be described as quadrangular-elliptical; their length is 0-050 — 0-056"™, and the breadth, 

 which is rather constant, the sphaerancora being almost unvarying as to form, is ca. o-028 ram . A few 

 developmental forms were found, showing the same kind of development as in the preceding species. 

 On account of the difference as to size and the peculiar form of the sphaerancora, its younger develop- 

 mental forms may easily be distinguished from the corresponding developmental forms of the large 

 ancora. 2. The large an corse are also similar to the ancorae in M. clliptica, but they are a little 

 more robust. Their length is 0-057 — cro78 mm , and the breadth is 0-021— 0-025™™. 3. The small ancorse 

 are of a similar form, their length is 0-024 — 0-030™™, and the breadth 0-007 — o-oio mm . Quite singly 

 aneorae may be found which seem, as to size, to form transitions between the two sizes of ancorae. 

 Of both forms developmental forms were seen, but only in slight numbers. All the microseleres occur 

 throughout the sponge and in the dermal membrane; here, again, the sphserancorse are seen in large 

 numbers in the membranes of the canals. The large ancorse occur in this species in larger numbers 

 than in the preceding one, and the three forms are about equally frequent. 



In the dermal membrane cellules spheruleuses > are found copiously; they are seen, partly as 

 distinctly limited cells of a size of about o-oi5 mm , partly gathered to heaps of granules. They are 

 colourless in spirit, with large, round, highly refracting granules. 



Remarks: This species was established by Schmidt I.e. as Desmacidon emphysema, but with 

 a description that rendered it impossible to recognize it; the sphaerancora he took to be a diatom. 

 As I have examined Schmidt's type specimen, I have been able to identify the species with cer- 

 tainty-. Thiele 1. c. has also examined Schmidt's species and has already shown it to be a 

 Melonanchora, but another species than clliptica. Thiele supposes that Fristedt's species is also 

 emphysema, which might also be indicated by Fristedt's description and figure; by examining his 

 specimen I have seen, however, that it is clliptica. On the other hand it is to be supposed from Vos- 

 maer's description and figure I.e. that he has had the present species before him. — In Bronn's 

 Klassen mid Ordnungen der Spongien» Vosmaer, at p. 127, mentions Melononchora 11. sp., and says 

 in a foot-note: Wird naher beschrieben in den zool. Resultaten der dritteu und vierten hollandischen 

 Nordpolexpeditiom. In Vosmaer' s work on the sponges of the Willem Barents expedition 1880 — 81, 

 however, only M. clliptica is mentioned, so that the author presumably has arrived at the conclusion 

 that the species was not different from this latter, what it must, accordingly, be supposed to have been 

 nevertheless. 



