154 ANIMAL KINGDOM. 



the under surface of the anterior part, fitted for grasping, and others behind 

 these, for swimming. In the Caligus group the species resemble 176, but the 

 mouth is trunk-shaped and movable. In the Cypris group the animal is con- 

 tained in a bivalve shell, as in fig. 178, and they are hence called Ostracoids. They 

 are seldom a quarter of an inch long* In the Daphnia group the body has a 

 bivalve shell as in Cypris, but the shell does not cover the head or close at the 

 margin. In the Limulus group — containing the Horseshoe of the sea-coasts of the 

 United States — there is a broad, shield-like shell, and a number of stout legs, the 

 basal joints of which serve for jaws. In the Phyllopod group the form is either 

 shrimp-like, approaching Cyclops, or like Daphnia or Cypris ; but the append- 

 ages or legs are foliaceous and excessively numerous : the name is from the Greek 

 for leaf-like feet. In the Cirriped or Barnacle group the animal has usually a 

 hard, calcareous shell, and is permanently attached to some support, as in the 

 Anatifa (fig. 179) and Barnacle. The animal throws out a number of pairs of 

 slender jointed arms looking a little like a curl, and thus takes its food, — 

 whence the name, from the Latin cirrus, a curl, and pes, foot. The Anatifa 

 has a fleshy stem, while the ordinary Barnacle is fixed firmly by the shell to 

 its support. 



Trilobites.— The Trilobites (fig. 177, and also 245 and 320, 322), 

 which occur only fossil, have a resemblance both to the Entomos- 

 tracans and the Tetradecapods. The similarity to fig. 174 (a Serolis) 

 among the latter is apparent; but they are supposed to be still 

 nearer the Entomostracans, and especially the group called Phyl- 

 lopods, in which the legs are thin-foliaceous and very numerous, — 

 for no remains of legs are found with any Trilobites, which would 

 not be the case if they had had the stout legs common to Crus- 

 taceans of the same size. It is possible that the abdomen (c d, 

 in fig. 177) had, beneath, a series of appendages; and, if so, they 

 differed from all known Entomostracans, and approximated to the 

 Tetradecapods. The division of the body longitudinally into three 

 lobes, to which the name trilobite refers, is in some species very in- 

 distinct, and there is in no case more than a mere depression and 

 suture. 



In the Trilobite the shell of the head-portion (a b, fig. 177) is usually called 

 the buckler; the tail- (or properly abdominal) shield, when there is one (fig. 320), 

 the pygidium. The buckler (a b) is divided by a longitudinal depression into 

 the cheeks, or lateral areas, and the glabella, or middle area (fig. 177). The cheeks 

 are usually divided by a suture extending from the front margin by the inner 

 side of the eye to either the posterior or the lateral margin- of the shell. In 

 fig. 177 (Calymene Blumenbachii) this suture terminates near the posterior outer 

 angle. The glabella may have a plane surface, or be more or less deeply trans- 

 versely furrowed (fig. 177), and usually with only three pairs of furrows. 



Worms. — Worms are divided into — 



(1.) JDorsibranchiates, or free sea-worms, having in general short branchial 

 appendages along the back. Many swim free in the open sea, and others live in tha 



