912 BRITISH MARINE ALG. 
curious brownish-red variety of this Callithamnion, called C. horridulum 
(from the curled or prickly appearance of its crowded branches), which, 
like the typical species, I never failed meeting with all around Plymouth, 
especially during the summer months, in the sheltered bays near Bovisand 
when the tide was gently flowing in. The rare and curious C. cruciatum 
is found on mud-covered rocks on the southern shores of England 
and Wales. I took this species in abundance, many years ago, in 
two or three situations in Plymouth Harbour. The fronds, which are 
about 3in. high, are divided into a number of long erect branches, 
which are occasionally furnished with a second and even third series ; 
the ramuli on all being crowded at the tips, giving the plant a remarkably 
feather-like appearance. The ramuliare usually pinnated or winged, and 
are set on each joint of the branches in pairs, and sometimes more 
numerously, but always exactly opposite; an arrangement which (in addi- 
tion to the division of the tetraspores, which are four-parted or cruciate) 
is referred to in the specific name of this plant. C.owmilum, taken in 
Miltown Malbay, in Ireland, and once by me up the river Plym, is a small 
variety of this species; the ramuli are much more closely set on the 
branches, and the joints of the stems and branches are shorter. C. 
floccosum is a rare early summer annual, found at the Orkneys and on 
various parts of the Scottish shores. I have had most lovely specimens 
sent me from Peterhead, some bearing favelle in abundance, and others. 
full of tetraspores. The fronds of this species are densely tufted, but 
sparingly and distantly branched. The branching is alternate, but every 
joint of the stem and branches throws out from each side of the upper 
shoulder, a pair of opposite, very short and slender, bristle-like ramuli. 
The tetraspores are borne on each side of these little ramuli, seated 
on short pedicles or stalks, as seen at b, Fig. 195, which represents a 
magnified portion of stem, branch, and fruited ramulus. The colour is a 
brownish-red ; the whole plant is very flaccid, and adheres very well to 
paper. A highly magnified fruited branch of C. Turneri is represented at 
c, Fig. 195. The fronds of this small species are rarely 2in. high. They 
grow in little bushy tufts on several species of seaweeds on various 
parts of the British coasts. The joints of the stems and branches are of 
much greater length than almost any other species of Callithaminion, 
and the branches are consequently very far apart, but, as well as the 
ramuli, invariably opposite. ‘The favelle, which are very similar to those of 
Grifithsia setacea (Fig. 192), are produced on stalks, and are enclosed in an 
involucre, or clasped by several tiny incurved ramuli. The colour is rose- 
red, turning a duller tintin drying. C.barbatum, so named from the small 
beard-like ramuli which clothe the upper parts of its long straggling 
branches, is a plant of such rare occurrence, that during the many years I 
have searched the shores of this country, I have met with but a solitary 
specimen. It is said to grow at Weymouth and Penzance, and should 
be looked for on mud-covered rocks, near low-water mark. The fronds 
are about 2in. high; the branches, which are opposite, but sometimes 
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