PORIFERA. II. 



125 



44 Lat. N., but on the eastern side of the ocean it is known no farther south than to the coasts of 

 England. It is not found in deep water, the greatest depth known being ca. 70 fathoms. 



Remarks to the synonymy. This species is generally enumerated as palmata Jolmst., and Carter 

 (1. c.i having examined Johnston's type specimen and found the characteristic chela, the identification 

 may also be regarded as sure. The species may, however, with certainty be traced farther back, 

 Ehlers (1. c.) having shown by examination of Esper's type specimen of Spongia digitata that this 

 species is identical with Johnston's palmata, what was also indicated by Esper's figure. Therefore 

 there might be some reason for taking up Esper's name of digitata, which dates from 1797. I have 

 not done so, however, as there is great probability that Spongia palmata Ellis and Solander, 1786, is 

 the same species. The description, to be sure, gives no hold, but the figure of the exterior, showing 

 the characteristic compression, seems to show, even if not quite certainly, that the question is of the 

 present species. Linne's name of Spongia ba cilia r is, on the other hand, cannot be taken up, as it is 

 impossible to decide, whether he has had before him the present species or some Pachycha lina-iorm. 

 - By the examination of Schmidt's type specimen of Pachychalina compressa I have been able to 

 decide that this species is identical with H. palmata, as already mentioned in part I of the Porifera of 

 the Ingolf-Expedition, p. 6. 



Group 2. Myxilleae. 



Megasclera generally divided into two forms, those forming the dermal skeleton, and 

 those forming the main-skeleton. Typically the skeletal spicules are monactinal and the dermal 

 spicules diactinal, but exceptions from this rule occur. 



It seems to be a rather important character of the group Myxillece that the skeletal spicules 

 are of one form and almost always monactinal, the dermal spicules of a different form and most fre- 

 quently diactinal. The reach of this character, however, cannot yet be decided. In the group Mycalece, 

 to be sure, instances may be found where the spicules that in some way or other belong to the dermal 

 membrane are smaller or of a form somewhat different from those of the principal skeleton, for instance 

 .17. placoidrs, some Espcriopsis-species, Artemisina, Homceodictya flab elisor mis, but they are generally of 

 the same type. In the following subfamily, Ectyoniiur, which is closely allied to Myxillece, on the 

 other hand, some genera are still found showing the difference, characteristic of Myxillecr, between 

 the dermal spicules and the skeletal ones, and still here the system is scarcely a natural one. 



The dermal spicules in Myxillece are generally briefly stated to be diactinal; this statement, 

 however, is not quite correct. As will be mentioned in the following under the single species the 

 equi-ended dermal spicules, whether they be strongyla, tornota, or tylota, are only secondarily diactinal, 

 but really monactinal, as they are begun as monactinal and grow as such to about their full length, 

 and then the final form only occurs by degrees, contemporaneously with the growth in thickness. In 

 the not quite developed spicules this development may still be traced, the ends being not quite equal, 

 and it is no rare fact that the ends upon the whole never become quite equal, but it may still be 

 decided in the fully developed spicules, which end has been the original point. The general fact is, 

 accordingly, that the finer, i. e. the younger, the dermal spicules are, the greater is the difference 



