Or THE NORTH-POLAR EXPEDITION. 241 



The only Ctenostomatous species is represented by one or two 

 imperfect specimens parasitic upon Bugula fruticosa. These, 

 moreover, are so few and so much, injured and overgrown by 

 Diatoms, that it is impossible to give an accurate definition of 

 the form, which does not appear to resemble any British species 

 with which I am acquainted, nor does it correspond with Leidy's 

 description and figure of Bowerbankia gracilis. In case it be new, 

 it might be termed Farrella, or, if with a gizzard, perhaps 

 Bowerbankia arctica. 



DESCRIPTION OF PLATE XIII. 



Fig. 1. Bugula fruticosa, Packard. Portion, enlarged 25 diam. 



2. Flustra serrulata, n. sp. Forked branch, of nat. size. 



3. „ ,, Another small piece, of natural size. 



4. „ „ A portion, magnified 25 diam. 



5. Eschara perpusilla, n. sp. A forked branch, magnified 25 diam. 



6. Cellepora cervicornis, Busk. Bifurcating branched portion, of natural 



dimensions. 



7. A zocecium of C. cervicornis, enlarged 50 diam. 



8. Zocecium of same, also magnified 50 diam, 



9. Farrella arctica, n. sp. Portion, enlarged 25 diam. 



On the Classification of Gasteropoda. — Part II. By John Denis 

 Macdonald, M.D., F.B.S., Inspector Gen. E.N". (Commu- 

 nicated by G. E. Dobson, M.B., F.L.S.) 



[Read November 18, 1880.] 



The Scutibranchiata, which were in my former system* incor- 

 rectly associated with the dioecious Grasteropoda, have been 

 arranged in the above revised Table with the other Grasteropoda 

 Monoecia. 



The conscientious naturalist, like the theologian, is always in 

 quest of the truth ; and consequently, if he finds that this has 

 been arrived at by one or many workers, it need not be sub- 

 verted for the pure sake of change, or of presenting a subject in 

 a more novel garb. I have therefore adopted the very natural 

 and simple distribution of the Scutibranchiata given by Dr. Gray 

 in his ' Guide to Mollusca,' carrying out an alteration which he 

 has himself suggested, and the propriety of which has indepen- 

 * See ' Transactions of the Linnean Society,' vol. xxiii. p. 69 (1860). 



LINN. JOURN. — ZOOLOGY, VOL. XV. 19 



