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Show 1895.] HYDEACHNID FOUND IN COENWALL. 175 The habitat of the creature is somewhat curious ; it was found in a very small stream of fresh water, just where it comes tumbling over the granite cliffs and runs down the sands into the sea. The part where the Mites were found was tbe bottom, not the top, of the cliff; the stream there is distinctly fresh water, but is only three or four feet above high-water mark at the high spring-tides ; so that when the wind is on shore and the sea at all rough considerable quantities of salt-water must be carried into the stream, and even at ordinary times a good deal of salt spray must reach it. I searched in vain for the Acarid higher up the same stream, and I have not hitherto succeeded in finding it in any of the other streams in the same district. Although a Water-Mite, it is not found swimming ; like other members of the genus it is adapted for crawling only ; but I have not ever seen it crawling on the bottom or on the water-plants, although of course it must do so. I have invariably found it either in small chinks and splits in the rock, where it can only be discovered by carefully chiselling away the rock in likely places, or clinging to the underside of large stones lying in deep pools ; I thought from the latter position that the Acarids had been carried down the stream, but, as before stated, I was not able to find them higher up. The Mite is very conspicuous when its hiding-place is discovered ; it is of a beautiful scarlet colour shaded and varied with orange, and the soft cuticle is diversified by a number of porous plates of clear yellow chitin sunk a little below the general level of the skin, so as to form shallow depressions. The legs are one of the most striking features, as most joints are furnished with a radiating whorl of large yellow spines tipped with scarlet, wiiich give a very brilliant appearance; the colours are difficult to preserve after death. The Acarus appears to belong to the genus Thyas, the principal characters of which are as follows:-Hydrachnidae with the eyes placed at the side of the body (far apart), with two-jointed mandibles, without swimming-hairs on any of the legs, and with the dorsal cuticle furnished with numerous separate chitinous plates. It is by the last-named character that the genus is finally distinguished from Kramer's genus Aturus. I propose calling the new species Thyas petrophilus, from its habits of life. THYAS PETBOPHILUS, n. sp. (Plate VII. figs. 1, 2.) o*. ?• mm. mm. Average length including rostrum about l'OO 1*35 „ „ of rostrum only about *10 *15 Greatest breadth about *65 '70 „ thickness, dorso-ventrally, about '40 *50 Length of le,„g, s , 2143sntrthd p a„i r abo„u t -*-5368085 1-'-65815005 |
