COMMENTARY. Coray correctly states in his ‘Notes on the Fragment of Xenocrates,’ that, in the ancient classification of animals, the ὀστρακώδη or ὀστρακόδερμα, were divided into the σκληρόστρακα, or testacea, comprehending oysters, muscles, &c.; and the μαλακόστρακα, or crustacea, comprehending the crabs, paguri, &c. But, as he remarks afterwards, the σκληρόστρακα were often called by the generic term, ὀστρακόδερμα. The ancient division of the lower classes of animals is derived from Aristotle’s ‘History of Animals’ (iv), and with some slight modifications it is the same as the classification adopted by Baron Cuvier. Pliny thus distinguishes the mollusca, crustacea, and testacea: “Piscium quidam sanguine carent, de quibus dicemus. Sunt autem tria genera: in primis quæ mollia appellantur (_mollusca?_): deinde contecta crustis tenuibus (_crustacea?_): postremo testis conclusa duris (_testacea?_). Mollia sunt, loligo, sepia, polypus, et cetera ejus generis,” &c. In another place, however, he introduces confusion by applying the term mollia to the crustacea. This mistake probably originated in the resemblance between the Greek terms μαλάκια and μαλακόστρακα. (Hist. Nat. ix.) We may mention further, that, in Oppian’s delightful poem on ‘Fishing,’ the crustacea are described at book i, l. 259, the testacea at l. 283, and the mollusca at l. 638. On the terms used by Ælian, see ‘De Nat. Animal.’ (ix, 6, ed. Schneider.) Athenæus gives a long disquisition on these animals in the third book of the ‘Deipnosophistæ.’ Of the testacea described by the ancient writers on dietetics, we are inclined to refer the chema to the genus _chema_ of modern naturalists, comprehending several species of the cockle: the purpura to the _helix ianthina_ or purple fish, in particular: the solen to the genus _solen_ or bag-fish: the spondylus to the genus _spondylus_ or prickly oyster: the buccina to the _buccinum harpa_: the cochlea to the _helix pomatia_ or edible snail: the astacus to the _astacus fluviatilis_ or crawfish: the pagurus to the _cancer pagurus_ or common crab: and the cancer to some variety of the same: the _locusta_ to more than one species of the _locusta_ or lobster; the squilla to the _crangon vulgaris_ Cuv. or shrimp: and the leo marinus indefinitely to the genus _cancer_. We think it but right, however, to confess that our own acquaintance with this department of natural history is not so extensive as to warrant us in speaking authoritatively on these matters.