76 Part I1I.—Twenty-siath Annual Report. 
Genus Chondracanthus, De la Roche. 
Chondracanthus Williamsoni,* sp.n. Pl. IIL, figs. 8-17. ; 
In this species the body is depressed, and of an ovate form when seen 
fromabove. Length about 7:5 millimeters, greatest width equal to about 
half the length. The head, which is articulated to the thorax, is subquad- 
rangular in its general outline, but has a shallow rounded projection on 
each side, as shown in the figure (fig. 8). There is only a slight con- 
striction between the cephalon and the thorax, and the neck is very short. 
The thorax, which is considerably depressed, has the lateral margins 
coarsely crenulated, or lobate; there are about six rounded but somewhat 
irregular projections or lobes on each side, the second and the last three 
being more prominent than the others. The posterior end of the thorax 
also terminates in a narrowly rounded median lobe, as shown in the 
figure (fig 8). The abdomen is much reduced in size and of a rounded 
form. 
The antennules are small, uniarticulated, and rather rudimentary in 
structure (fig 10). 
The antenne are moderately large, and each consists of a stout basal 
part, to which is articulated a strong terminal hooked spine, the whole 
appendage thus forming a powerful grasping organ (fig. 11). 
The mandibles are similar to those observed in other species of 
Chondracanthus : they consist each of a very short basal joint, and a 
terminal and broadly falciform masticatory part, both edges of which 
are finely serrated (fig. 12). The dilated appendage, armed with two 
short stout spines, situated at the base of the mandible, represents the 
maxilla (see fig. 12). 
Both pairs of maxillipeds are very small. The first pair are very 
similar in structure to those of Chondracanthus cornutus ; each consists of 
a moderately stout base and terminating in a straight claw-like spine, finely 
setose on the inner edge (fig. 13). 
The second pair are rather larger than the first ; they each consist of 
two joints of nearly equal width, but differing slightly in length, and 
armed at the apex with a short and claw-like spine and a small rounded 
process, as shown in the drawing (fig. 14). 
There are only two pairs of thoracic limbs ; both pairs are rudimentary, 
and are also similar in structure. Each limb consists of a short and 
broad basal part, gibbous on each side, which bears a small oblong process, 
separated from the basal part by a narrow constriction (figs. 15-16). 
The ovisacs were not very slender, and appeared to be of moderate 
length, but they were more or less incomplete. 
Figure 9 represents a young female which, though resembling the adult 
in having the lateral margins coarsely crenulated, differs in ‘being pro- 
portionally narrower. 
The male of this species is somewhat similar in form and structure to 
that. of Chondracanthus cornutus (O. F. Miiller), It is considerably 
dilated in front, but tapers towards the eee: end (fig. 17). The 
male is very small, being rather less than the 4, of an inch in length. 
The colour of this form is opaque white with a slight trace of red. 
Host Sebastes norvegicus (Ascan.), from Aberdeen Fish Market, 
February 1908. Several specimens were found in the angles formed 
by the gill cover and gill-arches, with the claw-like antenne of the 
specimens firmly fixed in the tissues of the host. 
* After my colleague, Dr. H. C. Williamson, to whom I am indebted for this 
and several other species. 
