ON BRITISH MARINE ZOOLOGY. 253 
On the Scottish coast this region is remarkable for prolific and peculiar 
species. Great numbers of Brachiopoda ( Terebratula Caput-serpentis, and 
-Crania norvegica) are found in gravelly and stony places. Dentalium en- 
talis, Nucula nucleus, Astarte suleata, Leda caudata, and (in places) L. pyg* 
mea, Mactra elliptica and Modiola modiolus, are all very prolific. ! 
Between 40 and 60 fathoms, on the verge of the region of deep-sea corals, 
we have too little experience on the English coast to judge. Cardium sue- 
cicum, however, essentially a northern form, was noted as abundant at a depth 
of 50 fathoms between Cornwall and Ireland. _ 
In the Scottish seas between these depths, besides most of the species noted 
as prolific in the last region, we find Nucula tenuis, Cardium suecicum, Nu- 
eula decussata (locally) and Venus fasciata abundant; also Turritella in 
places. Below that depth, Leda caudata, Syndosmya intermedia, Venus 
ovata and striatula (var.), Lucina spinifera, Dentalium entalis, Turritella, 
Ditrupa and Echinus norvegicus, have been taken in considerable numbers 
in several Scottish localities. Widely diffused species of Twrritella, Denta- 
lium, Modiola, Nucula, Venus and Astarte, appear to be most prolific through- 
out the range of their distribution. 
Generic and subgeneric groups confined to particular zones in depth.—In 
the Littoral and Laminarian zones, we find all the species of certain well- 
marked natural groups assembled, but very few, if any, of those which are 
distributed in the regions of corallines and of deep-sea corals are peculiar, 
the species of mollusks in the lower zones especially, being members of 
genera which have representatives in the Laminarian or in both Littoral and 
Laminarian zones. Within the two higher zones we find all the British 
species of Patella, Purpura, Littorina, Otina, Conovulus, Truncatella, Ca- 
lyptrea, Lacuna (except L. crassior), Aplysia, Scrobicularia and Donax. 
Almost, though not entirely confined to them, are also the genera Phasianella, 
Mya, Lutraria, Mytilus, Pholas and Cytherea. Some important genera, 
such as Rissoa, Chiton, Trochus, Mactra, Venus, Bulla and Cardium, are 
mainly developed in the Laminarian zone. In the genus Patella we have one 
section, that of Patella proper, confined to the Littoral zone, and another, 
Patina, confined to the Laminarian zone. The subgenus Hydrobia of Rissoa 
is almost wholly littoral. Very rarely do we find instances of a species 
strietly littoral descending far into the Laminarian zone or below it; on the 
west coast of Anglesey Purpura lapillus was dredged in 10 fathoms, and 
three specimens taken at that_depth were remarkable for the development 
and perfection of the crenulated laminz of growth on the surface of the 
shell. issoa Barleii of Jeffreys appears to be a variety of the littoral 
Rissoa ulve, descending below its usual level. More frequently do we find 
mollusks and radiata of the Laminarian zone and the upper part of the region 
of Corallines ascending into the littoral belt. This is especially the case in 
certain localities on the Hebrides, as in Skye and on the west coast of Ar- 
gyleshire ; and very generally is it to be observed, as the registrar pointed out 
to the Natural History Section in 1836, in the immediate neighbourhood of 
those localities where alpine plants, such as Silene acaulis &c., are found 
abundantly near the water’s edge. 
Certain genera, such as Neera, Crania, Pilidium, Cemoria and Propilidium, 
have, so far as the area under review is concerned, a range in depth entirely 
confined to the Coralline region and that of deep-sea corals. But elsewhere 
species of these genera ascend into the Laminarian, and possibly some of them 
into the Littoral zones, so that great stress cannot be laid upon their distri- 
bution as genera indicative of depth. Very important, however, are the 
᾿ facts stated with regard to the Laminarian and Littoral genera; and the geolo- 
