On North-American Thalassinidea and Astacidea. 299 there are four or five species of this genus. The second genus, SioUczharia^ is without pores or has them micro-scopically developed, the internal tubulation being remarkably close ; it contains two species. The sections of these spheres present microscopical appear-ances second to none in their beauty ; and the polarizing apparatus enables cleavage-and other lines of a non-organic nature to be distinguished. I must apologize for this brief notice ; but as the details are about to be published by the Indian Government, I am not at liberty to anticipate too much. Sept. 5, 1878. XXXV. — Remarks upon the Thalassinidea and Astacidea of the Pacific Coast of North America, with Description of a new Species. By W. N. Lockington. TSALASSINIDEA. Family Gebidae. Gebia pugettensis, Dana. Gebia pugettensis, Dana, U.S. Ex. Exp., Crust, i. 510, pi. xxxii. fig. 1 ) Stimpson, Crust. & Ecliin. P. S. N. Am. p. 48. This species is exceedingly abundant in San Francisco and Tomales Bays, and frequently attains a length of six inches or even more. The subterranean passages made by it are usually nearly perpendicular, about an inch across, and very neatly rounded in section, with the walls smooth as if plastered, the smooth-ness resulting entirely from the pressure of the animal's body as it pushes itself upwards and downwards by the action of its terminal abdominal segments. The burrows are not confined to strata of sand, but are abimdant also in mud, in sandy shingle, and even among rocks, ranging upwards almost to high-water mark, and downwards to at least three or four fathoms, since large speci-mens were brought up in abundance by the dredging-machines in Oakland Harbour. Almost every specimen collected in Tomales Bay, in the month of May, bore upon its abdominal feet either the curious Isopod Vhyllodurus abdominalis (Stimpson, op. cit. p. 71), or a small bivalve mollusk, Pijthina rugifera, Carpenter.
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