Dr. Strahl on the Thalassine. 459 
XLIX.— Supplement to a Memoir on the Thalassine*. 
By Dr. Stranrf. 
Amoncst the reasons cited by De Haan (‘Fauna Japonica,’ p. 160) 
in favour of the union of the Astacoidea and the Thalassinoidea, 
the relation of the simple branchia to the fifth pair of feet plays 
a not unimportant part. He states that although the <Aséa- 
coidea possess this single branchia, which is wanting in all Tha- 
lassinoidea, the genus Astacus itself belongs by its species to 
both sections, and effects the union. Subsequently, however, 
Erichson divided the genus Astacus, employing for this purpose 
especially the characters of the branchiz ; so that, by this division 
into new genera, the separation of the Astacoidea and Thalas- 
sinoidea might appear to be again established. The genera 
Cambarus and Cheraps, which are destitute of the branchia on 
the fifth pair of feet, and were therefore removed from the 
genus Astacus, nevertheless approach more closely to Astacus 
and its allies than to the Thalassinoidea. Cheraps even gives 
up another character of the Astacoidea, namely, the appendages 
on the first segment of the abdomen in the male sex, which 
are likewise wanting in the genera Astacoides and Engeus, and 
makes another step towards the Thalassinoidea; nevertheless 
its relationship to Astacus and its allies is greater than to the 
Thalassinoidea. The common characters of the genera grouping 
themselves immediately about Astacus, besides the perfectly deve- 
loped antennal scale (armiger and squama), are, that the first three 
pairs of feet are didactyle, and the external lamina of the caudal 
fin transversely divided ; the forehead bears a rostrum projecting 
over the eyes, beneath which the latter are concealed whenever 
the appearance of danger causes them to require protection. 
Here belong the genera, Homarus, Nephrops, Paranephrops, 
Astacus, Astacoides, Engaus, Cambarus, and Cheraps. I propose 
to group these together as Astacina. 
Glaucothoé and Asius are not to be placed here, although 
they are stated to possess the antennal scale; at any rate, they 
have fewer didactyle feet, and the outer lamina of the caudal fin 
is entire. In describing Aaius plectrorhynchus, I have pointed 
out the difficulty which existed in determining whether this spe- 
cies does or does not possess a moveable scale. It now appears to 
me doubtful whether Azius and Glaucothoé have a moveable scale, 
because the existence of this belongs to the general character of 
the Astacina, from which both these genera depart in several 
respects ; and, indeed, they cannot even be referred to a common 
* See ‘ Annals,’ May 1862, p. 383. 
+ Translated by W. S. Dallas, F.L.S., from the ‘ Monatsber. der Akad. 
der Wiss. zu Berlin,’ February 1862, p. 133. 
