ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 51 



Tanganyika Crustaceans.* — Mr. W. T. Caiman describes two species 

 of macrurous crustaceans collected in Lake Tanganyika by Mr. J. E. S. 

 Moore. One forms the type of a new genus (Limnocaridind) allied to 

 Caridina, the other is probably a new species of Palsemon. The most 

 striking and important character of the new genus is the reduction of 

 the branchial system ; there are only four gills, and no epipods at all. 



North American Caridea.j — Prof. J. S. Kingsley gives a key for 

 the identification of the shrimps and prawns reported from the waters 

 of North America, north of the soutbern boundary of the United States 

 and within the 100-fathom line. It is believed that this key will serve 

 for the identification of any species (except in the genera Hippolyte 

 and Pandalus) now known to inhabit American waters ; but the student 

 may reasonably expect that several tropical species may later be found 

 witbin these limits. The genera most likely to furnish additions of 

 this character are Alpheus, Palsemon, Peneus, Atya, and Caridina. 



North American Astacoid and Thalassinoid Crustacea.! — Prof. J. 

 S. Kingsley contributes on this subject one of the useful synopses of 

 North American Invertebrates which are appearing in the American 

 Naturalist. 



North American Fresh-water Ostracods.§ — Mr. C. H. Turner con- 

 tributes to the series of synopses of North American Invertebrates a 

 key to the fresh-water Ostracods. The key includes all fresh-water 

 genera known to the author, whether represented in America or not, 

 and it aims at including all the known American species. 



Eyes of Polyphemidae.|| — Dr. Otto Miltz publishes an elaborate 

 memoir on this subject, having for its special object the manifestation 

 of the connection between the structure and special function of the 

 remarkable eyes of this family. Their special peculiarity, as already 

 known, lies in the fact that they are divided into dorsal and ventral 

 halves of very different structure. The details of structure are de- 

 scribed for a number of genera, the most general result being to show 

 that it is in the genus Polyphemus that the nearest approach is made to 

 the typical Daphnid condition. This is shown by the fact that at the 

 posterior border of the eye short thick crystalline cones and rhabdomes, 

 with extensive pigmentation, are present as in a typical Daphnid, while 

 the special Polyphemid modification, consisting in the elongation of 

 cones and rhabdomes, and the limitation of pigment to the vicinity of 

 the retina, only appears gradually on the ventral surface. From the 

 conditions seen in Polyphemus, those found in the genera Podon and 

 Evadne can be derived ; but the eye of Leptodora seems to have had an 

 independent Daphnid origin. 



As to the value of the Polyphemid condition, an increase in the size 

 of the eye and of the number of cones increases the power of sight, as 

 does also a diminished divergence of the cones. As increase in absolute 

 size has obvious limits ; the end is better attained by diminished diver- 

 gence. For physical reasons this is best confined to a certain number 



* Proc. Zool. Soc. London, 1899, pp. 704-12 (2 pis.). 

 t Amer. Nat., xxxiii. (1899) pp. 709-20 (57 figs.). 

 t Tom. cit, pp. 819-24 (S figs.). § Tom cit., pp. 877-88. 



[| Biblioth. Zool. (Leuckart and Chun), xi. Heft 28 (1899) pp. 1-60 (4 pis.). 



E 2 



