Dr. Strahl on the Thalassinse. 459 XLIX. — Supplement to a Memoir on the Thalassinse*. By Dr. STRAHLf. Amongst the reasons cited byDe 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 Asta-coidea possess this single branchia, which is wanting in all Tha-lassinoidea, the genus Astacus itself belongs by its species to both sections, and efi^ects the union. Subsequently, however, Erichson divided the genus Astacus, employing for this purpose especially the characters of the branchiae ; so that, by this division into new genera, the separation of the Astacoidea and Thalas-sinoidea might appear to be again established. The genera Camharus 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 Engceus, 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, Engceus, Camharus, and Cheraps. I propose to group these together as Astacina. Glaucothoe and Axius 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 Axius 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 ^a?ms and Glaucothoe 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. t Translated by W. S. Dallas, F.L.S., from the * Monatsber. der Akad. der Wiss. zu Berlin,' February 1862, p. 133.
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