ILaguna Ratine Laboratory 177 



SOME MARINE AND TERRESTRIAL ACARINA 

 OF LACUNA BEACH 



HABEY V. M. HALL 



During the summer we picked up quite a series of mites, many of 

 them new species. From this material I describe the following mites 

 which are mostly marine or littoral. Among them the Gamasidae 

 are represented by a species that is parasitic on the large beach 

 amphipods, a Sarcoptid was taken from one of the birds, the Trom- 

 bidida? are represented by a large red Ehyncolophid common on the 

 dry sand of the upper beach, the Hydrachnids by a new marine 

 species and the Halicarida? by three new species. In the last two 

 families good series were obtained but only by means of much towing 

 and patient search. 



Seius orchestoideae n. sp. 



(Figure 96) 



Length without rostrum 641 micrrn., 542 micrrn. ; width 410 micrm., 

 320 micrm. Length of legs one and four about 520 micrm. ; length of 

 legs two and three about 400 micrm. Color of female light straw, 

 that of male still lighter ; smooth but not polished. Dorsal plate en- 

 tire and covering whole dorsum. Shape ovoid, the anterior end some- 

 what sharper (especially so in the male) and the posterior end 

 rather flattened (also most marked in the male). Body broadest one- 

 third of the way from the posterior end. The outline form 'above 

 runs to the rounded anterior point without any shoulder-like bulge 

 in either sex. Dorsal surface evenly convex. Mandibles greatly 

 retractile (shown extended in the figure but can be drawn wholly 

 within the body). Both arms of chela? short, stout. The fixed arm 

 with a terminal beak proximal to which is one other tooth; the 

 movable arm has two teeth which fit between and proximal to those 

 on the fixed arm. From the movable arm and pointing outward 

 and forward is a cylindrical process slightly swollen at the end in 

 the male but not so swollen in the female. This process is about 

 the same diameter as one of the leg-spines measured at the base 

 of such a spine. Coxa3 almost contiguous and legs long, without 

 apophyses in either sex ; all legs sparsely set with short, stout spines 

 and terminated by short caruncles with claws on all legs. Dorsal 

 surface with a few very heavy spines, over twice the diameter of 

 those on the legs and placed as follows: (except for the first pair 

 at anterior margin and close together, all these spines are directed 



