NOTES ON CRUSTACEA FROM FAIRLIE AND HUNTERSTON. 353 
Thalestris forficulus, Claus.—This is a very distinct species of 
Thalestris. The branches of the first thoracic feet are long and 
slender in comparison with those of most of the other members 
of the genus; it is also a small species. A few years ago we 
described, under the name of Vhalestris forficuloides, a Copepod 
that seemed to be different from Claus’s species, but both my son 
and I are now inclined to regard this as merely a local form of 7’. 
Sorficulus. 
The two apparently undescribed Copepods found in the Hun- 
terston pools are both very slender and both appear to be rare. 
Only four specimens of the larger and rarer of the two have 
been observed, but specimens of the smaller form were somewhat 
more frequent. These smaller specimens were difficult to notice, 
because they so closely resembled the bits of fibre with which 
they were mixed up; it was on this account easy to miss them, 
and therefore they may have been less rare than they appeared 
to be. 
Another Copepod, which I have recorded as Delavalia gies- 
brechti, var., resembles that species very closely. The typical 
D. giesbrechtt was discovered in Ayr Bay about two years ago, 
It has a peculiarly broad terminal seta on each of the caudal 
furca, and it may be distinguished by this character alone. In 
the Hunterston variety the caudal setz are of the usual form. 
The arrangement of the setz on the fifth thoracic feet also differs 
slightly from the typical form, but it agrees in so many other 
points, that it seems better, for the present at least, to consider it 
as a local variety of D. giesbrechti than to make a new species of it. 
Among other doubtful Copepods is an Harpactid that partakes 
somewhat of the characters of Canthocamptus cuspidatus and 
Moraria popper, but it differs from them in various ways, but 
especially in the form and armature of the fifth thoracic feet, and 
I have not yet decided what to make of it. 
These intermediate forms are very troublesome to the 
systematist. Their differences are such that they cannot very 
well take their place beside species already described, yet their 
affinities with them are so close that one hardly knows where to 
place them, or what characters to fix upon in order to discriminate 
them from others. This is where the chief difficulty in the study 
of the Copepoda comes in. | | 
