ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 677 



coloui' varieties which are constant. But one form occasionally obtained 

 was so distinct and so remarkable that it is described as a new and 

 distinct species or sub-species, D. argentatum. In size, general shape, 

 processes of head and thorax, it is indistinguishable from D. hercules, 

 but the head, thorax, legs, etc., are jet black. The elytra are pale 

 plumbous, silvery grey, or white with a silvery metallic sheen, edged 

 and spotted with black. This form was found on the interior mountain 

 ranges of the island. 



Orthoptera of Paraguay.* — J. A. G. Rehn gives a record, with 

 in many cases descriptions, of the non-saltatorial and acridoid Ortho- 

 ptera of Sapucay, Paraguay. Seven new species are described, and in 

 many cases notes on the variability of series, both in size and coloration, 

 have been given. The region is evidently very rich in species of 

 Ortho])tera. 



Note on Assortative Mating.f — Vernon L. Kellogg describes the 

 case of the ladybird beetle, Hippodamia convergens, an insect of much 

 variability as to its dorsal colour pattern. An opportunity occurred 

 (unfortunately interrupted by an earthquake) of studying their mating, 

 and particular attention was given to the question as to whether it was 

 assortative. The evidence, as far as it goes, indicates that the matings 

 were wholly non-selective ; they are chance matings — that is, follow the 

 law of probability. The relative proportion of numbers of the different 

 colour types determines the matings ; they are, therefore, not assortative. 



5. Arachnida- 



Spider Threads.^ — J. R. Benton has made a series of experiments 

 to test the strength and elasticity of spider- thread. He finds that the 

 material of the thread possesses quite a high tensile strength, about 

 double that of most kinds of wood. The results of these experiments 

 differ so greatly from those of Beaulard on the mechanical properties of 

 silk, that the investigator concludes that the material of spider-thread is 

 not identical with silk, as is sometimes asserted. 



New Oribatidae from the United States. § — -Nathan Banks de- 

 scribes twenty-four new species of Oribatidse from various parts of the 

 United States. This fauna appears to be similar to that of Europe, with 

 the exception of one or two peculiar genera. There is a larger percentage 

 of smooth genera, as Galumna, Oribatula, and fewer of the roughened 

 types, as Notaspis, Nothrus, and Cepheus. The genus Pelops, repre- 

 sented in Europe by ten or twelve species, has not yet been found in 

 North America. 



Bionomics of Pycnogonidse.H — J. C. C. Loman gives an account 

 of the habits and life-history of this group, especially of those members 



* Proc. Acad. Nat. Sci. Philadelphia, lix. 1907, pp. 151-92. 

 t Science, xxiv. (1906) pp. 665-6. 

 j Amer. Journ. Sci., clxxi. (1907) pp. 75-8. 



§ Proc. Acad. Nat. Sci. Philadelphia, Iviii. (1906) pp. 490-500 (5 pis.). 

 II Tijdschr. Nederland Dierkund. Vereen., 2nd Series, April 1907, pp. 254-82 

 (24 figs.). 



2 Y 2 



