K5S CEYLON 1'EAUL OYSTER REPORT. 



), a sponge from tlie China Sea, in which lie also discovered isochelve. This 

 specimen seems to resemble the Ceylon form very closely, and it is possible that 

 future investigations may show theiii all to be specifically identical. 

 H.N. 212 (deep water outside pearl banks, Gulf of Manaar). 



SUB-FAMILY : ECTYONINyF, 



Desmacidonido3 in which some of the megascleres take the form of spined styli, 

 originally developed as echinating spicules of the skeleton fibre or projecting at 

 right angles from the substratum. 



The members of this sub-family are usually easily recognised by their spined styli, 

 but, as in the case of perhaps every type of spicule, the spined styli may be lost 

 again by degeneration. Such degeneration has obviously taken place in the genus 

 Rftspailia, which, until recently, has been confounded with the Axinellidre. As a 

 rule, microscleres are present in the form of isocheloe (to which toxa are frequently 

 added), but these also may be lost. 



Myxilla, SCHMIDT. 



Ectyoninre, usually of massive, irregular form, in which the megascleres are spined 

 styli, which may or may not be echinating, and variously ended diactinal forms 

 which typically belong to the dermal skeleton. The typical microscleres arc 

 tridentate isochelfe, to which other forms may be added. 



This genus in a certain sense occupies, as pointed out by Mr. RIDLEY and myself 

 in the Report on the " Challenger " Monaxonida, a position intermediate between the 

 sub-families Esperellinfie and Ectyonime, including both species with definite echinating 

 spicules and species in which such spicules cannot be distinguished from those of the 

 ordinary skeleton reticulation. It appears probable, from their form, that the spined 

 styli originated in the first instance as echinating spicules, i.e., spicules in which the 

 growth of one end (the base) became arrested by pressure against a firm substratum, 

 while the apex projected freely into the surrounding soft tissues and thus formed an 

 internal defence against the attacks of parasites. In some species these echinating 

 spicules appear to have passed into the main skeleton and form a reticulation with 

 one another.* It appears desirable, therefore, to regard the presence of spined styli (or 

 tylostyli) as constituting the leading feature of the Ectyoninae, without insisting too 

 strongly upon their actual arrangement. 



In the genus Myxilla itself it is sometimes impossible, owing to the irregular 

 character of the skeleton reticulation, to distinguish sharply between echinating and 

 non-echinating styli. and, as I have pointed out before (10), I cannot, therefore, agree 

 with TOPSENT (62, &c.) and HANITSOH (46) in retaining GRAY'S genus Dendon/.r for 

 species in which no special echinating spicules are recognisable. 



* Compare l!liiilnli'mni<i i/n/ini and its relationship to the thin eiirnistiiiij forms of the same genus. Sec 

 ,-vlso below, under Mji.nlln 



