Page:VCH Norfolk 1.djvu/217

 CRUSTACEANS sometimes greenish, sometimes brightly mottled with reds and browns, with the advantage of not being disguised by shaggy hairs. Small as it is, the diversified denticulation of its carapace gives it a look of distinction. The other crabs of the quartette in question are species of Portunus. The members of this genus have habits and functions which are hinted at in the trivial names, swimming crabs, fiddlers and cleansers. When an in- solent fellow proposed to appoint Epaminondas to be chief scavenger, the great Theban general promised that even in such an office he would take care to serve the state efficiently. Great and small among Crustacea grandly render us this service in aquatic realms, and the Portuni are called cleansers only because they are a little more conspicuous than the rest in doing this work. Most crabs are able to swim, but the Portuni and some others have an advantageous modification of structure for this purpose. The hindmost legs, instead of an awl-like ending, have the last two joints flattened out, to form, as it were, fins or oar-blades, by help of which rapid motion through the water is accomplished. Also these joints in action, being geniculated or bent one towards the other, produce some resemblance to the motions of a fiddler's elbow. In this genus, and like- wise in Pirimela, it will be noticed that the pleon or infolded tail part of of the male has only five segments distinct, whereas all the seven are distinct in the female. Portunus pusillus (Leach) occurs all round England, chiefly in moderately deep water. Metzger reports it from twelve and fifteen fathoms on the Norfolk coast.' The title of dwarf fin crab, or dwarf swimming crab, well suits an animal of which, according to Bell, the ordinary length is one-third of an inch, though the measurements of its carapace may occasionally swell to four-fifths of an inch in length by a full inch in breadth.* The carapace is rugose and irregularly granulated, having the regions well marked, the lateral dents not very acute, and the three-lobed front well advanced, with the middle lobe projected beyond the other two. Portunus holsatus (Fabricius), reported by Metzger from twenty-three fathoms depth on this coast,' besides being considerably larger than the largest Portunus pusillus, has a much smoother carapace, with sharper lateral teeth, the front not advanced, and its middle tooth not projecting teyond the others. Attention may here be called to the circumstance that all the crabs that have been mentioned have the normal five more or less acute lateral teeth or ' dents,' with the exception of Cancer pagurus, in which the dents become broad shallow lobes, nine in number. In the tribe of the Oxyrrhyncha, or sharp-beaked crabs, two species were taken by the German expedition on the coast of this county, both at the same station and in the same depth as the Pilumnus and Pirimela previously noted. One of these is Hyas araneus (Linn.). This, by its specific name, attempts to monopolize the title of spider-crab, which is often applied to all the members of its tribe. Adam White calls it the 185
 * Nordseefahrt der Pommerania, p. 295. * Bell's British Stalk-eyed Crustacea, p. 114.
 * Nordseefahrt der Pommerania, p. 294.