known as Asellus aquaticus. 201 
although the animal has been fully described and figured by 
various author s, no one until recently appears to have suspected 
that the individuals belonged to more than one form or species. 
In a recent paper, however, Monsieur EK. G. Racovitza * has 
pointed out that under the name Asellus aquaticus two quite 
distinct forms or series of forms have been confused, and that 
these differ distinctly from one another by several fairly we!l- 
marked characters. He adopts the name Asellus aquaticus, 
Linné, 1758, for one species which appears to be the com- 
monest and the only one hitherto fully described and figured ; 
for the other, which is therefore new, he suggests the name 
Asellus meridianus. For a full account of the differences 
between these two and for excellent figures showing them 
reference should be made to M. Racovitza’s paper. It seems 
desirable, however, to call the attention of English naturalists 
to his results, and in doing so it will be sufficient to indicate 
briefly some of the more important differences. They are as 
follows :— 
A, aquaticus, A, meridianus. 
Antenna 2., Malealmostaslong ashody, Two-thirds length of body 
female a little shorter. in both sexes, 
Mazxillal ., Four plumose setze on distal Five plumose sete on distal 
margin of inner lobe. margin of inner lobe. 
Pereopod 1 . Adult male with large tri- Inferior margin of propod 
angular projection on in- almost straight, no pro- 
ferior margin of propod. jection. 
Pereopod 4. Carpus with longitudiual Carpus with row of 10-12 
row of 4-5 spines, discon- long spines, continuous, 
tinuous. 
Pleopod 1 of Exterior margin of exopod Exterior margin of exopod 
male, emarginate. straight. 
Besides these there are other minor differences in the shape 
of the lateral margins. of the peraou segments II. to V. and 
in the second pleopods of both male and femaie animals. 
On receipt of M. Racovitza’s paper 1 examined the speci- 
mens in my own collection, and find that both forms are 
represented—namely, Asel/us aquaticus, 1umerous specimerts 
collected in the Edinburgh—Glasgow Canal at Edinbureh 
about the year 1898, others i in the "River Neckar, He idelbere: 
22. iv. 1900; Asellus meridianus, several specimens from a 
small brook at Tunbridge Wells, Mngland, forwarded to me 
by the Rev. T. R. R. Stebbing. I have dissected and ex- 
amined a male and a female from each of these localities, as 
it is almost impossible to distinguish the two species by 
* Archiv. Zool. Hixpér. et Gén. 1919, tome 658, Notes et Revue, 
pp. 31-43. 
Ann, & Mag. N. Hist. Ser. 9. Vol. v. 14 
