236 Mr. R. Gurney on 
Skull: condylo-basilar length 39°3 ; diastema 12°9 ; upper 
molar series (alveolar) 6°9; palatal foramina 6°3 x 3:3 ; 
palatilar length 19°5; least interorbital breadth 7°2 ; zygo-. 
matic breadth (app.) 20°8; median length of nasals 18°8 ; 
breadth of nasals anteriorly 5°0 mm. 
Specimens examined.—One, the type. 
XXXI.— Two new British Entomostraca: Alona protzi, 
flartwig, and a new Species of Mesochra in Norfolk. By 
RoBert Gurney, M.A. 
Alona protet, Hartwig. 
Alona protzi, Hartwig, Sitzber. Ges. Naturf. Freunde, 1900, p. 228; 
Keilhack, Arch. f. Hydrob. u. Hydrog. vi. 1911, p. 467. 
A number of specimens of this Alona were obtained on 
September 12, 1920, by washing masses of Cordylophora 
detached from the woodwork of Ludham Bridge, on the River 
Ant, in Norfolk. A strong current runs through this narrow 
bridge, and the water, in normal circumstances, is quite 
fresh, but the species of Entomostraca found in the collection 
included Nannopus palustris, Tachidius littoralis, and Mesochra 
rapiens—all species characteristic of more or less brackish 
water. Cordylophora grows in luxuriance on this woodwork, 
and I have on several occasions investigated the Hutomostraca 
living in its shelter without previously meeting with A. protzi, 
neither have I found it in any other locality. Nine days later 
only a very few individuals were to be found, and on 
November 17 the species had entirely disappeared. It would 
hardly be supposed that Cordylophora would provide a suit- 
able habitat for Entomostraca ; but six species of Cladocera 
and ten of Copepoda were found in collections made on 
Sept. 12 and 21. 
Alona protzi resembles A. guttata, Sars, but is readily 
distinguished by the presence of three denticles on the 
posterior ventral angle of the shell and by the structure of 
the postabdomen. The latter has a marked backward pro- 
longation, but the apex is rounded and not angular as in 
A, guttata. ‘The dorsal margin is armed with a double row 
of eight to ten small spines, and there are a number of lateral 
groups of very delicate hairs which do not quite reach the 
margin of the postabdomen. ‘The basal spine of the terminal 
claw is very long, exceeding half the length of the claw, and 
