264 THE VOYAGE OF H.M.S. CHALLENGEE. 



Tavria, Dana, distinct alike from H//pma, with which Spence Bate united it, and from 

 Metnecus, with which Boeck made it synonymous. Daira, Milne-Edwards, is altered by 

 Dana, on page 1596, to Dairilia, on the ground that Baira was preoccupied. This new 

 form of the name is incorrectly given as Dairinm in the British IMuseum Catalogue, owing 

 probably to the misprint in Dana's own work, on page 1442. It is given correctly on 

 pages 1519, and 1545 and 1604; Bovallius, 1885, says, "I am quite sure that Dana was 

 wrong in introducing the animals described by him into the genus Daira of Milne-Edwards;" 

 he is of opinion that Paraphronima, Glaus, comes nearest to, if it be not identical with, the 

 Daira of Jlilne-Edwards. Si/nojna, Dana, the single genus of his subfamily Synopinae, 

 must be transfeiTed to the Gammaridea, as Clans has already pointed out. In some of the 

 species of this genus, besides the confluent principal eyes to which the generic name refers, 

 there are two small subsidiary groups of ocelli ; hence the expression " pigmentum oculorum 

 unicum" in the generic character is unsuitable. 



For the readjustment of the other two families of the Hyperidea see Notes on Glaus, 1879. 



In treating of the Orchestidre, which he takes as the type of the Amphipoda (p. 849), Dana 

 describes in detail the head and its (theoretical) segments. He considers that the sides and 

 top of the head correspond to the iirst antennary and ophthalmic annuli, one or both ; that 

 the epistome and lateral plates adjoining it represent the sternal and episternal pieces of the 

 second antennary annulus [against which view see Spence Bate, British Assoo. Eeport, 1885, 

 p. 26] ; that the labrum and a lateral piece above the mandible represent the sternal and 

 episternal pieces of the mandibular annulus ; that the back piece of the lower part of the 

 head which supports the maxillipeds is the proper episternal of the maxilliped annulus, 

 while the first and second maxillary annuli are not represented, unless combined with the 

 maxUliped segment at the back of the head. 



Pages 1395-1413 contain an interesting essay on the classification of Crustacea. "The funda- 

 mental idea," the author says, " which we shall find at the basis of the various distinctions 

 of structure among the species is, the hiijher cenfraNxafion of the su^jerior grades, and the less 

 mncentrateii central forces of the inferior." " This centralization is literally a rephdlization 

 of the forces. In the higher groups, the larger part of the whole structure is centred in the 

 head, and contributes to head functions, that is, the functions of the senses and those of the 

 mouth. As we descend, the head loses one part after another, and with every loss of this 

 kind there is a step down in rank. This centralization may be looked for in the nervous 

 cords ; but the facts are less intelligibly studied there than in the members, the production 

 and position of which measure the condition of the forces." At the close he criticises the 

 names Podophthalmia and Edriophthalmia, on the ground that though all stalk-eyed 

 Crustacea may belong to the Podophthalmia, there are many sessile-eyed species which 

 cannot be grouped with the Edriophthalmia. In the classification which follows, pages 

 1414-1415, he renames his Subclass II., Tetradecapoda, which he thus defines :^" Annuli 

 cephalothoracis cephalici numero sejytem. Oculi sessUes. Appendices branchiales 

 simplicissima3, sive thoracicae sive abdominales. Cephalothorax multi-annulatus, carapace 

 carens, pedibus seriatis instructus. Abdomen appendicibus seriatis instructum, raro 

 obsolescens." The epithet simj^Hcissiinx applied to the branchial appendages must be 

 qualified in regard to some species of Amphipoda. 



The work concludes with an essay on the Geographical Distribution of Crustacea, pages 

 1451-1592, in which many interesting conclusions are deduced from the facts at Dana's 

 command. When he comes to speak (p. 1581) of the " origin of the geographical 

 distribution of Crustacea," he says, for the origin of the existing distribution of species 

 " two great causes are admitted by all, and the important question is, how far the influence 

 of each extended. The first, is original hn-al creations; the second, migration." The 

 form of his answer to this question would probably have been different had his book been 



