ISOPODS 



293 



logged timber, which without their destructive agency might become 

 serious obstructions to navigation. Limnoria is only the fifth of an inch 

 in length, and its back is covered with minute hairs, to which dirt usually 

 adheres. It burrows with its mandibles, or jaws, which are chisel-like 

 at the ends. Its habitat extends from a little above 

 to a little below tide-marks throughout the whole At- 

 lantic coast. 



GENUS Sphceroma 



S. quadridentatiim. The name of the genus 

 to which this species belongs is derived from the 

 peculiar habit of many of the species of rolling them- 

 selves into a ball when alarmed. The body is so 

 constructed as to admit of this singular change of 

 shape. The abdomen turns under ; and the last 

 abdominal appendages, together with the narrow 

 epimera, shut in the legs and cover the ventral 

 portions with armor. The body, when extended, is an ellipse a little 

 over a quarter of an inch in length and half that in breadth. The legs 

 are hairy and adapted to walking. The anterior abdominal segments 

 are fused into one, but are marked at the sides with depressed lines. 

 The abdominal feet are plate-like and fringed with hairs. A slight 

 elevation runs around the margins of the animal like a border. The 

 color is variable. Some are a uniform slaty gray ; others are marked 

 with a longitudinal patch of color on the 

 back. It is found from Cape Cod to Florida 

 among algae or rocks, and is easily recog- 

 nized by its habit of rolling itself into a 

 ball. SpJiferoma destructor is a boring 

 isopod, larger than Limnoria, and is even 

 more destructive, since its holes are larger ; 

 but its range is limited, or, at least, it has so 

 far been found only in the St. Johns River, 

 Florida. 



GENUS Idotea 



I. marina (Linnaeus), I. irrorata 

 (Edwards). This species is about one inch 

 long, and is easily recognized by the ab- 

 domen, the first three segments of which are 

 narrow and terminate in acute teeth, while the 

 other three are fused into one with straight 

 sides and ending in three teeth, of which 

 the middle one is the longest. The first pair 

 of abdominal feet are large, long, and plate- 

 like, covering the other'feet and whole under 

 surface of the abdomen like an operculum. 

 The head is nearly square, the eyes are 

 small, and the antennae have long peduncles. The articulations of the 

 thoracic feet are fringed with hair. The color of this species varies : 

 s.oinetirues it is light ox % dark green, or brown with black soots ; again 



Idotea marina. 



