532 ME. A. T. JEKNIWaS ON A 



Later in the same year Mr. Carter * was able to give a tui; 

 account of a specimen boring in a coral (AmpMhella oculata, 

 Duncan) dredged between Scotlaud aad the Faroe Isles. De- 

 ciding that the sponge could not remain in the genus Gummina, 

 he substituted for the name previously given that of Alectona 

 Mtllari. 



The genus has not yet been recorded as boring in molluscaii 

 shells, but there is a variety of A. Millari commonly found in 

 those o£ Lima excavata, Eabr., from Cliristiania and the Scandi- 

 navian coast. I have not yet observed it in any other shell, ever? 

 in collections from the same locality. 



Though not specifically distinct from the original type, this 

 form seems worthy of attention on account of certain peculiarities 

 in its mode of growth, and because it presents a striking instance 

 of the inclusion of foreign spicules. 



The Habit of the Sponge. — Scattered over the outer surface of 

 the shell are circular openings, irregularly distributed and variable 

 in size, leading into passages communicating with the chambers 

 excavated by the sponge. The larger are about ^-V i^^^ ^^ ^^^~ 

 meter, and the passages into which they open are lined by a thin 

 white crust. In many cases the opening is roofed over by a con- 

 vex white disk with a central perforation, and similar structures 

 are seen occasionally crossing the passages below the surface. 

 (PL XIII. figs. 3, 4.) 



On examination, these disks and the crust lining the passages 

 are seen to consist entirely of the flesh-spicules. 



In the region of the umbo the shell-substance has been eaten 

 through in irregular patches, and the spaces are now filled by 

 masses of spicules in which the flesh-spicules are far more 

 numerous than the megascleres. 



The question whether the sponge projected on the outside or 

 grew over the surface in this region is of some interest, as in the 

 original type there was distinct evidence of such an extension of 

 growth outside the coral. 



If there had been any such external growth, it is probable that 

 remnants of it would be left, seeing that the more delicate pa- 

 pillae over the small openings are still preserved. Moreover, the 

 predominance of flesh-spicules in these patches suggests the 



* Joiinial of the Royal Microscopical Society, vol. ii. 1879, p. -193, pis. xvii.- 

 xvii. A. 



