8.6 Walker-Arnott_, on Campylodiscus Hodgsonii. 
slide) in my Ipswich preparation. Three out of the four 
marked C. Hodgsonii, in SmitVs slide from Poole Bay^ belong- 
to it. I have seen it also from Arran^ and various other parts, 
so that it is much more common than the large kind^ if it can 
be so called. 
In the large one there are no canaliculi on the disk or 
central portion, and the granular strise are often very obscure, 
particularly after long boiling in acid. Smithes figure shows 
that they are placed in lines, but this arrangement is often 
so unsatisfactory in most specimens as to leave a justifiable 
doubt on Dr. Gregory^ s mind, if his C. eximius could be the 
same. The small one has the median line (?) sharp ; it is 
scarcely a line, but a strong plica or keel ; the canaliculi pass 
on almost to the middle line, being scarcely fainter on the 
disk than those of the margin, with which they are continuous 
and isometrical. The apparent separation between the disk 
and the margin is caused by a flexure or keel. If we were 
to suppose C. Ralfsii to have a flexure of this kind (to which 
there is an approach in figs. 52 and 53 of Dr. Gregory^s 
Clyde forms) , this small one would through it be more allied 
to C. Ralfsii than to the large C. Hodgsonii. 
" It thus appears that the C. eocimius, Greg., is the same as 
the large C. Hodgsonii of Smith, and the small C. Hodgsonii 
cannot be the same species. The large C. Hodgsonii is scarcely 
known, at least by that name ; that which is usually so called 
(and which was probably alone known to Dr. Gregory) is the 
small one. If Mr. Hodgson had found both, it might sufiice 
to give his name to the small one, and call the large one C. 
eximius ; but if he did not find the small one, there would be 
an absurdity in giving his name to the species not collected 
by him, in which case this last might be called C. Smithii.^' 
The foregoing extract from a letter received from Profes- 
sor Walker-Arnott, he has permitted us to bring before this 
Society. In his conclusion, as to the identity of the large 
C. Hodgsonii, Smith, and the C. eximius of Dr. Gregory, I en- 
tirely concur. I have specimens of the C. Hodgsonii from 
the River Cleddau, South Wales, from Lyme Regis, Wey- 
mouth, and Milford Haven, and find the markings in the 
central part of the valve in all states, from the distinct moni- 
liform radiant lines, described and figured by Professor Smith, 
to the faint and irregularly scattered granules, characteristic 
of C. eximius, and in some specimens hardly any discernible 
at all, with any object glass or variety of illumination. These 
variations also are not dependent on locality, as they occur 
in the same gathering, and I think therefore they aff'ord no 
sufficient grounds for separating two fbi'ms that agree so 
