134 Mr. R. Gurney on the Copepod 
XIV.—A Description of the Copepod Cylindropsyllus brevi- 
cornis, Van Douwe, and of a new Species of D’ Arcythomp- 
sonia, Scott. By Ropert Gurney, M.A. 
[Plates V.--VII. } 
CYLINDROPSYLLUS BREVICORNIS was first described by Van 
Douwe from two male specimens taken in brackish water at 
Greifswald, and a single female was found by Brehm in 1914 
in a collection made in fresh water at Sebenico in Dalmatia. 
In neither case did the material permit of the publication 
of a full description, and as I have had the opportunity of 
examining a number of specimens, and have come to the 
conclusion that a new genus should be formed for its 
reception, I think it advisable to give a further account of 
it with figures. 
Horse ta, gen. nov. 
Body vermiform, the abdomen not distinct from the thorax. 
Genital segment partly or wholly divided into two. First 
pair of antenne short, with few joints. Second pair three- 
jointed, without external ramus. Mandible without external 
ramus. Maxillipedes absent. Swimming-legs alike in both 
sexes, the internal rami of two and the external of three 
joints. Fifth pair of legs minute, one-jointed. 
A comparison of the single representative of this genus 
with Cylindropsyllus shows very striking differences in struc- 
ture, particularly with regard to the swimming-legs, Horsiella 
approaching in this respect more nearly to the genera 
Leptocaris and D’ Arcythompsonia. It differs from these two 
genera and also from Cylindropsyllus in the absence of the 
external ramus of the second pair of antenne and of the 
mandibles, and in the absence of the maxillipedes. 
Horsiella brevicornis (Van Douwe). (Pls. V. & VI.) 
Cylindropsyllus brevicornis, Van Douwe, Zool. Anz. xxviii. 1905, 
p- 487; Brehm, Zool. Anz. xliii. 1914, p. 337. 
Shape of body cylindrical and vermiform, as in Cylindro- 
psyllus; the first segment of the thorax marked off from the 
head by a slight dorsal groove exteuding partly down the 
sides. Integument thin and without markings. The genital 
segment is completely separated into two in the male, but 
in the female the line of division does not extend across the 
ventral surface. The fifth abdominal segment is twice as 
