158 Rev. T. Hincks's Critical Notes 



doctrine, and emphasizes a point vvhicli has lost the systematic 

 value it once possessed. 



The only permanently crustaceous Adeona with which I 

 am acquainted is the British species A. violacea. It shows 

 unmistakably its affinity to Microporellaj but is furnished with 

 goncBcia and is destitute of theooecium. Avicularian cells are 

 wanting, and the reproductive cells exhibit a somewhat lower 

 degree of specialization than we meet with amongst the fenes- 

 trate and branching forms. They are scattered over the 

 colony singly or in pairs (occasionally in larger number), are 

 about twice as large as the zooecia, slightly convex, and fur- 

 nished with a narrow, transversely elongate orifice. So far 

 as I have observed, however, there is little or no increase in 

 the number of pores. Rarely two are met with instead of one, 

 as in the zooecia ; but more generally there seems to be no 

 increase of number, though the size of the pore is much greater. 

 In the remarkable variety, however, which I have described 

 and figured from the Channel Islands * there are two pores 

 in the zocecia, and in the reproductive cells three or (com- 

 monly) four of considerable size f. 



2. Family MembraniporidsB. 



Memhranipora radicifera^ Hincks. 

 In this curious species the structure conforms to the Mem- 

 braniporidan type, but the mode in whicli the zoarium is 

 attached bears a general resemblance to that which prevails 

 amongst the CellulariidfB and Bicellariidge. A large number 

 of tubular fibres is emitted from the inferior surface of each 

 cell, so that the base of the zoarium is completely covered and 

 concealed by the multitude of these root-like appendages, 

 whicli penetrate into the ooze over which the polyzoon spreads, 

 and attaching themselves to fragments of shell, stone, &c., 

 hold it to its place. The adaptive modification is extremely 

 interesting, but, like the flexible stem of Adeona, it has no 

 special systematic value. We already know of one or two 

 similar cases, and probably many more exist J. But another 

 peculiarity (which is shared by the two species mentioned in 

 the footnote) has been observed in M. radicifera §. Its cells 

 are partially disjunct, each of them is connected with the 



* Hist. Brit. Mar. Polyzoa, p. 216, pi. xxx. fig. 3. 



t The differences between the var. and the normal A. violacea are so 

 important that 1 believe it should rank as a species. 



f 1 have described a similar structure in Unhrilina ferox, MacG., and 

 Schizoporella arc/entea, Iliucks (" Contributions Gen. Hist. Marine Poly- 

 zoa," ' Annals ' for July 1881 and March 1885. 



§ '' Contributions" &c., ' Annals ' for July 1881. 



