Mr. H. J. Carter on two new Calcispongiae. 5 



" Mr. M'Colla has furnished me with a variety from the 

 Irish coast that merits to be distinguished. The sponge rises 

 up in compressed sinuous leaf-like lobes, which are united 

 together so as to form a lobulated crust nearly an inch in 

 thickness, with a circular osculura on every projecting angle 

 (pi. 20. fig. 6). Were we to imagine that a cluster of Orantia 

 compressa had grown so close as to press against each other, 

 and the various specimens to have coalesced into one mass, 

 we would have a correct idea of this variety. That it is, 

 however, no variety of G. compressa, is proved by the differ- 

 ence of its texture as well as by the form of the spicula." 

 (Brit. Spong. 1842, p. 183.) 



I need hardly add, after this quotation, that Dr. Johnston 

 was acquainted with the species which I have now the plea- 

 sure to dedicate to his respected memory ; nor, on the other 

 hand, need I allude further to Dr. Bowerbank's description of 

 Leuconia nivea (Brit. Spong. 1866, vol. ii. p. 36) than to state 

 that, as he has changed Johnston's name of Orantia nivea to 

 Leuconia nivea, so he has lost sight of or ignored this classical 

 writer's description of the true Grantia nivea, and replaced it 

 by an imperfect one of his " variety." 



That, however, Johnston's " variety" is entitled to a distinct 

 appellation, the above description will show. 



As the great quadriradiate spicule of the surface of Leuconia 

 Johnstonii is but a larger form of that which is common to the 

 cloacal surface alone of most of the calcareous sponges, I have 

 given an illustration of that which is found in Grantia ciliata 

 as a type specimen (PI. II. fig. 32). It will be observed that 

 one ray is straight [h), while two others are more or less 

 curved and opposite to each other (a a) ; this is the common 

 form of the frnadiate spicule ; and it is in the straight ray 

 alone that a trace of the central or axial canal common to the 

 siliceous spicule is seen (c), which trace, however, is here the 

 central canal filled up with a cylinder of the same material as 

 the spicule, so that, in fact, there is no canal at all. The 

 fourth ray {d) projects at about right angles to the other three, 

 and sometimes is a little excentric — that is, arises from the 

 straight ray at a little distance from its union with the two 

 curved ones. This ray is also curved forwards (that is, towards 

 thevent), and in this way projects into and forms the armature 

 of the cloaca: it would have been opposite, probably, if the 

 current had been so, and hence is one of the structural evi- 

 dences of an aboriginal excretory stream. 



What is remarkable, however, in Leuconia Johnstonii is, 

 that this spicule is so large that its fourth ray not only pro- 

 iects in a formidable manner into the cloaca (PI. II. fig. 40, c c). 



