A. S. Packard Jr., on Insects inhabiting Salt water. 109 



long, bifid at the end, the upper fork being much the smaller, 

 especially on the anterior paii's, forming a small acute tubercle ; 

 in the middle of the under side of the claw (on all the feet) is 

 a brush of fine hairs of equal length, arranged in a single row. 

 On the penultimate joint of the anterior tarsi are five stout hairs ; 

 on the other tarsi three, the two proximal hairs being contigu- 

 ous. External female genitalia with two bivalve contiguous 

 plates, like those of B. formosa Dana and Whelpley, Length 

 •07 of an inch. The body of the young is whitish, longer, 

 more ovate than in the adult; the abdomen being a little 

 pointed behind. 



With the exception of Philippi's Pontarachna punctulatum 

 (Wiegmann's Archiv, vol. vi, p. 191, 1840, PL iv, fig. 4, 6), 

 which was discovered by him in the bay of Naples (he does not 

 state at what depth, consequently I infer that it was in shallow 

 water), the species under consideration is the only one which, so 

 far as I am aware, has been found to be exclusively marine. 

 The genus Pontarachna is very different from Hydrachna and 

 Thalassarachna, and I should judge that it rather approaches 

 Atax. It differs from Thalassarachna in the shorter, unarmed 

 palpi, and in the apparent (Philippi does not mention or figure 

 them) absence of a mandibular beak. The palpi are half as 

 long as the fore legs. 



The present species was dredged by Prof Yerrill in 20 fath- 

 oms, on Clark's Ledge, in Eastport Harbor. It wa^ found (four 

 or five specimens, young and adult), " on hydroids," &c. It 

 will be an interesting point to determine whether, like the other 

 species of the genus, it also lives in the earlier, or even in the 

 adult state among the gills of Lamellibranchs, and also whether 

 it lives between tide marks, thus agreeing with the distribution 

 of Chironomous oceamcu^. At any rate we have here an insect 

 and a mite breathing by tracheae, and extracting_ the oxygen 

 from the water at the great depth of 120 feet, and, in the case of 

 the dipterous larva, with no apparent variation from specimens 

 living at low-water mark. In this connection I might notice 

 the fact that we have on our New England and Labrador shores 

 several species of mites of the family Trombididse, which run 

 over seaweeds and live under stones between tide marks, and I 

 have observed similar species at Beaufort, N. C, and Key West, 

 Florida. 



As regards the distribution of the species of brine insects, 

 several questions of interest arise. How are we to account for 

 the origin of the Ephydra halophila in such prodigious quan- 

 tities in the vats of the Equality Salt Works of Illmois, a local- 

 ity remote from salt lakes and the ocean shores? Are the brine 

 species of the Salt Lakes of Utah and California, remnants of 

 an oceanic fauna, and of the tertiary period, or are they of re- 



Am. Jour. Sci.-TniRD Series, Vol. I, No 2.-Feb., 1871. 



