1882. ] PROF. F. J. BELL ON THE GENUS PSOLUS. 645 
be noted (1) that there is just as much imbrication in a large 
specimen from Massachusetts Bay, collected by the United-States 
Fishery Commission, and presented by the Smithsonian Institution ; 
(2) that taking the three Greenland specimens already referred to, we 
find a most obvious relation between the size of the example and the 
extent of the imbrication of the scales, the latter decreasing as the 
former increases ; (3) that the same phenomenon is to be observed in 
the series of Japanese specimens, a study of which leads one to the 
conclusion that the increase in the covering-capacity of the bivial 
armature is, at any rate, partly due to a diminution in the extent of 
the overlap of the different plates, At the same time it is to be 
remembered that the Japanese specimens examined are all smaller 
than any one of those from the Atlantic which I have had the 
opportunity of comparing with them. And this must be borne iu 
mind when the question of the range of distribution of this species 
again comes under discussion ; the writer who then treats of the matter 
will not, I trust, fail to carefully study the philosophical remarks on 
this subject which are to be found in Mr. W. Percy Sladen’s account 
of Captain St. John’s Japanese Echinoidea and Asteroidea’, where 
the importance of distinguishing the characters of forms with a wide 
distribution is most wisely insisted on. 
In addition to the indications of a wider distribution than was 
suspected for this species, the preceding discussion brings also into 
prominence the fact that younger are more strongly imbricated than 
older specimens, but that, so far as we can judge from a single 
example, the American race retains more than the European this 
overlapping of the plates. 
Just as the appearance of Psolus fabricii or a most closely allied 
form in the Japanese seas is a matter which need excite no wonder, 
so the second locality whence, as I fancy, the species is now for the 
first time recorded, only brings the species into the category of such 
circumpolar forms as Strengylocentrotus drobachiensis ; on the other 
hand, now that we know that the species is to be found at Kamt- 
ehatka, we are able to accept, with, as it were, a kind of personal 
experience, the fusion of P. sitchaensis, Brdt., with P. fabricii. 
PsoLus SQUAMATUS. 
Two magnificent specimens of this species, the longest 130 mm. 
long, from the Gulf of St. Lawrence, were presented in 1880 by 
Principal Dawson ; and their examination brings to mind the view of 
some naturalists that P. fabricii is nothing more than a variety of it. 
At the first sight of the British-Museum specimens, such a view 
would be warmly rejected; but now that we have learnt the kind of 
changes that occur in imbrication during growth, there would be no 
reason to imagine, even if we had not the figure of Koren, that 
P. squamatus in the young condition has the plates less imbricated 
than P. fabrictt. On the other hand, the granulation of the scales in 
P. squamatus appears to be closer and the grains smaller ; and I have 
1 Jour. Linn. Soc. xiv. (1879) pp. 429-434. 
? Of. Duncan and Sladen, op. cit. 
