NEW BRITISH ENTOMOSTRACA. 233 



consisting of two slender, hispid, linear branches — unjointed, but 

 bearing long apical and latei'al setae — with a nipple-shaped 

 prominence separating their bases (PL XXXIX. fig. 6). Caudal 

 rami slender, bearing three terminal setse, and one near the 

 middle of the posterior margin (PI. XL. fig. 7) ; copulatory 

 organs of the usual complex type (fig. 8) ; ejaculatory duct encased 

 in a very dense and massive capsule (PI. XXXIX. fig. 7) ; whorls 

 of the duct very indistinctly visible through the fibrous covering. 



Female unknown. 



Of this remarkable species I have seen only one example, a 

 male. It was found unexpectedly on a re-examination of some 

 material collected many years ago in ditches by the side of the 

 River Arun, near Arundel, the water being, no doubt, slightly 

 brackish. The shell was so much encumbered with muddy 

 debris that it could not be distinctly seen, my attention being 

 drawn to it by the remarkably strong projection of the male 

 organs below the margins of the valves. The animal presents 

 characters intermediate between the Cyprididee and Cytheridse, 

 the three pairs of ambulatory legs corresponding to those of the 

 Cytheridae, while the following pair and the post-abdominal 

 rami are like the similar structures in Cyprididae. But there is 

 in addition to these limbs a remarkable biramose appendage 

 which was detached in the process of dissection, but was probably 

 derived from the body of the animal close to the anterior legs. 

 This structure I take to be possibly homologous with one described 

 by G. 0. Sars * under the name " processus piliferus," and stated 

 by that author to be found between the feet of the first pair in the 

 male of Bairdia suhdeltoidea. Other noteworthy characters are 

 the presence of a pair of rodlike sensory appendages on the ante- 

 penultimate joint of the antennae, and the hispid clothing of the 

 anterior legs and "processus piliferus." 



I regret very much that no further specimens of AruTiella are 

 to be found in my collected material, but must hope that some 

 future collector may be fortunate enough to find it, and thus be 

 able to place the species on a more secure basis. It must 

 evidently be hunted on the muddy bottoms of the ditches, its 

 swimming powers being to all appearance non-existent, 



EXPLANATION OF THE PLATES. 



Plate XXXVIIL 



Diaptomus pusillus. 



Fig. 1. Female seen laterally, X 84. 



2. Male seen from below, X 84. 



3. Abdomen of female, with attached spermatophores, X 140. 



4. Foot of fifth pair, female, X 300. 



5. „ „ male, X 140. 



6. Distal joints of right anterior antenna of male, X 240. 



* 'Nj'e Bidrag til Kundskaben om Middelhavets Invertebratfauna,' p. 128, 

 pi. xviii. fig. 12. 



Proc. Zool. See— 1913, No. XVI. 16 



