ZOOLOGY. 61 
Mr. Regan concludes his remarks on these fishes as follows :—‘ The fact that in so 
many cases species may be paired is more in harmony with the view that there has 
been a gradual modification during isolation than with the supposition that a mutant 
has arisen which has replaced the parent form.” 
The twenty-six plates include figures of seventy-eight of the 415 species enumerated. 
The Maps inserted in the Introduction showing the distribution of certain families are 
worthy of attention. 
9. TERRESTRIAL and FiuviatineE Mo.uusca: by E. v. Martens. 
In this volume the author summarizes the characters and distribution of the species 
in common Tables, instead of giving separate descriptions. The geographical distri- 
bution is given at great length in the ‘ Introduction’ (published in 1901), accompanied 
by separate Tables of the Terrestrial and Freshwater genera. The difference between 
the fauna of the Pacific and Atlantic slopes is noticed, but is stated to be not very 
important as regards the land shells. Central Guatemala (Baja Vera Paz), however, 
is said to be occupied chiefly by metamorphic rocks, while North Guatemala (Alta 
Vera Paz) is mostly of limestone formation: this difference accounts for the greater 
richness of land shells in the latter province. One peculiarity of the fauna of the 
Pacific slope is worthy of note, viz. the occurrence of large sized Otostomi and Bulimult 
in Western Mexico related to various Andean forms, the distribution being somewhat 
analogous to that of the majority of the Cactacee. The submarine Mollusca of the 
eastern and western shores are said to be distinct, more so than some truly marine 
shells, but there are some remarkably analogous forms among them. 
Of the forty-four plates belonging to this subject, the first twenty-eight are 
coloured. 
[The Crustacea have not been studied. 
The FresHwaTerR Matacostraca were undertaken by Prof. T. H. Huxley, 
but his contribution was never finished. | 
10. ARACHNIDA ARANEIDEA. Vol. I.: by the Rev. O. Pickard-Cambridge. 
This volume contains descriptions and figures of 417 new species of Araneidea, and 
a list of species identified by the author. The new forms are illustrated on the thirty- 
nine coloured plates. 
11. ARAcHNIDA ARANEIDEA and Opruiones. Vol. II.: by F. O. Pickard-Cambridge. 
Vol. II. of this subject gives the systematic arrangement of the whole of the species 
of Arancidea described in Vol. I. and the large number added in Vol. II. A synopsis 
of the Families is given on pp. 541-544. The ‘Opiliones,’ or ‘ Harvestmen,’ are 
dealt with on pp. 546-585, and illustrated by three plates, LIL—LIV. ‘The author is 
unable to say very much about the general distribution of the Araneidea, the material 
