26 PLATE XI. 



secondary spicula of the interlacing portion of the 

 structure. X 25 linear. 



In the " Last Report on Dredging among the 

 Shetland Isles," ' British Association Reports ' for 

 1868, p. 329, the Rev. A. M. Norman proposes to 

 make this species the type of a new genus, and to 

 designate it Quasillina, and he thus characterises the 

 genus : 



" Sponge consisting of a single, clavate, hollow body, 

 widening upwards from the base, and rising at once 

 from the surface of the stone to which it is attached, 

 without any expanded basal mass. Skeleton, beauti- 

 fully reticulate, primary fasciculi ascending in parallel 

 straight lines from the base, and in diverging, radiating 

 lines from a central mammaeform projection at the 

 summit of the sponge ; secondary fasciculi at right 

 angles to the primary ones. Spicula fusiform! - 

 acuate." 



I cannot concur in the idea of separating this species 

 from the rest of those comprised in the genus Poly- 

 mastia, and with which it is in perfect accordance with 

 every one of their common anatomical characters. 

 The inhalent and exhalent organs occupy the same 

 relative positions in the sponge, and even the forms 

 and position of the spicula are the same as those of 

 the greater number of species of Polymastia. The 

 author of the proposed new genus does not, in the 

 characterisation of QuasiUina, show the slightest ana- 

 tomical difference from Polymastia; and the only 

 difference between them, on which he grounds his 

 reason for making P. brevis into a new genus, is that 

 the " sponge consists of a single, clavate, hollow body, 

 widening upwards from the base, and rising at once 

 from the surface of the stone to which it is attached 

 without any expanded basal mass." These characters 

 founded on external form apply correctly enough to 

 the single, outsized, abnormal specimen on which his 

 description is based, but they do not apply with equal 

 correctness to the series of ordinary-sized specimens 



