. 
674 The American Naturalist. [August, 
As to a color-sense in spiders, the authors are of the opinion that 
their experiments, while not conclusive, yet all taken together, strongly 
indicate that spiders have the power of distinguishing colors. (Trans. 
Wisconsin Acad. Sciences, Vol. X, 1895.) 
Classification and Geographical Distribution of the Nai- 
ades.—In his study of the fresh water pearly muscles, Mr. Simpson 
finds that the division of these mollusks into two families, Unionidæ 
and Mutelidee, founded on the completeness or incompleteness of the de- 
velopment of the siphons, cannot stand. He accordingly diagnoses the 
two families on the basis of the shell characters, and finds that his dis- 
tinctions fully agree with what is known of the facts of geographical 
distribution of the paleontology of the Naiades, and the classification 
of v. Ihering, based on the characters of the embryos. The Unionide, 
as defined by the author, include the genera Unio Retzius, Anodonta 
Lamark, Prisodon Schumacher, Tetraplodon Spix, Castalina v. Iher- 
ing, Burtonia Bourguignat, Arconaia Conrad, Cristaria Schumacher, 
Lepidodesma Simpson, Pseudodon Gould, Leguminaia Conrad and 
Solenaia Conrad. In the Mutelide he places the following genera :— 
Mutela Scopoli, Chelidonopsis Ansey, Spatha Lea, Pliodon Conrad, 
Brazzea Bourguignat, Glabaris Gray, Iheringella Pilsbry, Monocon- 
dyiæa d'Orbigny, Fossula Lea, Mycetopoda d’Orbigny. 
The author considers the relationship between these two great groups 
as not a very close one. The Unionide are characterized by schizodont 
teeth and a glochidium embryo. The Mutelide have taxodont teeth, 
and, so far as is known, the embryo is a lasidium. 
Mr. Simpson finds that the Naiades are capable of being grouped into 
assemblages of related forms which have a more or less immediate 
common ancestry ; and on the basis of this grouping they are distri- 
buted into eight provinces, as is shown in the following table: | 
( Europe. 
Northern and Western Asia. 
North Pacific to the Desert. 
Pacific drainage of North America. 
Palearctic, . 
Ethiopi i o -.. 5. Africa south of the Sahara, 
ś Asia south of the Himala 
Oriental, f East Indies to the seny Islands. 
: Australia. 
Australian, Tasmania. 
New Zealand. 
Neotropical, . . . . South America. 
