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. 



