SESSILE-EYED SERIES 



3241 



thoracic segments being all of about the same size and shape, and their appendages 

 short, stout, and used for walking. The anterior segments of the abdomen are 

 short, and the posterior fused into a caudal shield. The species 

 of the genus Idotea live in shallow water, and frequent places 

 where there is an abundance of decomposing seaweed. They are 

 essentially carnivorous, feeding on dead fish, worms, and mollusks. 

 The tribe Flabellifera contains part of a 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 illustration given. 

 In the genus Serolis, which alone represents the family Spoa , r0 ma (enlarged). 

 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 to the 

 caudal plate. Their nourishment appears chiefly to con- 

 sist of the organic materials distributed in the fine sand, 

 diatomacea and organic detritus. Their locomotion is 

 carried on less by swimming than by backward move- 

 ments on the sandy ground, wherein the widely sepa- 

 rated 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 Sphceromidce the convex body is cap- 

 able 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, be- 

 neath stones or among seaweed at low water. The next 

 family (Gnctthiidce} contains the genus Gnathia, in which 

 the males and females are so dissimilar that they were 

 referred to two families. In the adult the male mandi- 

 bles are powerful and prominent, and the head is large, 

 squared, and at least as wide as the thorax. In the adult 

 female, on the contrary, the head is small and triangular, 

 without visible mandibles, and the thorax is much di- 

 lated. Many species are known from the European 

 coasts, and one has been obtained at a depth of nine 

 hundred fathoms. Belonging to this tribe, but repre- 

 senting a famity by itself, is Limnoria lignorum, known 

 to fishermen as the gribble, which is a persistent destroyer 



of submerged wood. The creatures are about one-sixth FEMALE GNATHIA. 

 of an inch long, and of an ashy gray color; and the de- (Enlarged.) 



MAI.E GNATHIA (enlarged). 



