MR. LUBBOCK ON SOME FRESHWATER ENTOMOSTRACA. 208 
PONTELLAD.E. 
DIAPTOMUS. 
The remarks above made with reference to Cyclops are to a certain extent applicable 
also to the genus Diaptomus. Müller described three species, under the names D. cæ- 
ruleus, D. rubeus, and D. lacinulatus; but the characters which he gives have been 
regarded as unsatisfactory by most of those who have subsequently written on the genus. 
S. Fischer, however (Bull. de la Soc. des Nat. de Moscou, 1853), has described two very 
distinct species, which he refers to Müller's C. cerulea and C. lacinulata. The Cyclopsina 
lacinulata of Fischer is probably our 2. castor; and his C. cerulea resembles in many 
respects a new species, which I have now to describe, and which I propose to call after 
Mr. Westwood, the founder of the genus. 
DrAPTOMUS WESTWOODII, n. sp. F 
The cephalothorax consists of seven segments, of which the second is the largest, and 
the last is quite short. Seen from above, the cephalothorax of the male resembles the 
figure given by Baird, but it ends in a small spine (Pl. XXXI. fig. 5.) : in the female the 
posterior segment is expanded and ends in two spines (Pl. XXXI. fig. 1); it resembles, 
therefore, the figure given by Liljeborg (J. c. pl. 26. fig. 1). 
The anterior antenne consist of twenty-six segments, and are in the male as long as, 
and in the female rather longer than the body. The terminal segment is small. The 
apical and subapical setze are subequal in size. The penultimate, antepenultimate, and 
the preceding segments have each of them a long hair at the posterior side. The hair at 
the anterior side of the apex of the penultimate segment is large; the corresponding 
hairs on the two preceding segments are about as long as the segments to which they 
belong, while that on the twenty-first segment is again much larger. All these hairs, 
except the usual lanceolate* one at the apex, are plumose. The left antenna of the male 
resembles that of the female; but the right is swollen and prehensile. The sixteenth, 
seventeenth, eighteenth, nineteenth, and twentieth segments are specially enlarged for 
the reception of the powerful flexor muscle; and most of the setze on them are shortened 
and thickened. 
The bend takes place between the twentieth and twenty-first segments. The twenty- 
first and twenty-second segments have coalesced so completely, that, but for the eo 
ment of the setze and the analogy with D. castor, they might have been taken as a single 
segment. The twenty-third and twenty-fourth have united in a similar manner, and the 
latter bears a sort of tooth at its apex. On the seventeenth, eighteenth, and nineteenth 
segments one of the setæ assumes the form of a rod with a hook at the end. 
* M. Schultze (Arch. fiir Naturgeschichte, 1862, p. 356) attributes the observation of these lanceolate hairs to 
M. de la Valette, in 1857, and Leydig, in 1860. As Jong ago, however, as the year 1853 (Ann. & Mag. of Nat. Hist. 
P. 160, &c.) I had called special attention to these peculiar appendages, and pointed out that they held certain 
definite positions, although I did not hazard an opinion as to their exact function. Again, Mr. 50 Bate, in his 
“ Report on the British Edriophthalma," published in the Journal of the British Association for 1855, p. 29, describes 
them under the name of ** membranaceous or auditory cilia "—a name which sufficiently indicates his views as to 
their use, 
