274 



CRUSTACEANS. 



The tribe Flabellifera contains a part of marine species, in which the abdomen 

 terminates in a tail-fin, formed as in the macrurous decapods from the telson and 

 the limbs of the last segment. There are too many families to mention, but some 

 of the characteristic forms are shown in the accompanying illustrations. In the 

 genus Serolis, which alone represents the family Serolidce, the body is depressed 

 and broad, the segments of the thorax being furnished with long pointed side- 

 plates, which impart to the animal a superficial resemblance to a trilobite. The 

 legs and two pairs of antennae are long. It is stated that the Serolidce " live by 

 preference on sandy ground, into which they burrow with their flat bodies up 



Serolis bromleyana (nat. size). 



to the caudal plate. Their nourishment appears chiefly to consist of the organic 

 materials distributed in the fine sand, diatomacea and organic detritus. Their 

 locomotion is carried on less by swimming than by backward movements on the 

 sandy ground, wherein the widely separated feet are used as a point of support." 

 The species figured (S. bromleyana) is the largest, and has been taken at a depth 

 of nineteen hundred and seventy-five fathoms. In the SpkderomidcB the convex 

 body is capable of being rolled into a ball. Several species of Sphceroma occur 

 on the coasts of Britain, and may be found, sometimes in numbers, sometimes 

 isolated, beneath stones or amongst seaweed at low water. The next family 

 (Gnathiidce) contains the genus Gnathia, in which the males and females are so 



