Scientific Intelligence*— Zoology* 187 
of P. islandicus , I judge it expedient to institute a comparison 
between the two species, after the manner in which I have com- 
pared P. niveus with P. rearms , the only species to which it ap- 
proaches in its characters. P . islandicus has from 70 to 100 or 
more * ribs ; P. niveus has invariably 46 *f* ; in the former , the 
ribs are very irregularly grouped, from 2 to 6 being crowded 
together, with smaller ones intervening, but without any regu- 
larity ; in the latter , they are beautifully regular ; in P. islandi- 
cus , they are marked with very numerous, delicate, erect laminae, 
or scales, without anv appearance of echinations; in P. niveus , 
they are compact and smooth, with scattered echinations toward 
the margin of the shells ; I J . islandicus is a tolerably thick shell, 
of a pale reddish colour, with concentric circles of a deeper tint ; 
P. niveus is a very thin shell, of a pure white colour : P. islan- 
dicus has a margin singularly irregular in its teeth, recalling the 
idea of that sort of leaf which is term ed folium crispatum ; P. 
niveus has its marginal teeth as regular as those of a cockle. 
If, after this, P. islandicus and P. niveus should be considered 
identical, then assuredly, P. maximus and P. jacoboeus are so 
also ; and scarcely any two species of a genus can be named, that 
must not, on the same grounds, be mere varieties. I now sub- 
join the distinctive characters of the three species. — P. islandi- 
cus, testa suborbiculari rubente, fasciis concentricis saturatiori- 
bus, radiis circiter 100 varie aggregatis rotundatis lamellulis den- 
sissimis scabriusculis. P. niveus , testa orbiculari, fragili Can- 
dida, radiis 46 subcompressis rotundatis sparsim breviter tenui- 
terque echinatis. P. varius , testa orbiculato-oblonga, colore va- 
ria, radiis 32, obsolete, squamosis, subcompressis, rotundato-pla- 
natis, sparsim crasse echinatis. — W. M C G. 
39- Balls in the Stomach of Fishes. — A globular substance is 
found on the shores of the Mediterranean, which has much re- 
semblance to the balls of hair formed in the stomach of oxen, 
goats, and some wild animals, but which appears to be produced 
by an agglomeration of the leaves of zostera marina in the sto- 
* In a specimen in the Museum of the University of Edinburgh, the number is 
104 ; in a very perfect specimen belonging to W. Nicol, Esq. Edinburgh, the num- 
ber is 106. 
+ That is to say in 32 specimens. 
