ANIMAL KINGDOM. 123 



which occur only fossil, have resemblances both to the Entomostracans 

 and to the Tetradecapods. The similarity to Fig. 164 (a Serolis) among 

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

 Entomostracans, and especially the group called Phyllopods, 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 Crustaceans of the same size. It 

 is possible that the abdomen (c d, in Fig. 167) had, beneath, a series 

 of appendages ; and, if so, they diffei'ed from all known Entomostra- 

 cans, 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 indistinct ; 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. 167) is usually called the 

 buckler; the tail- (or properly abdominal) shield, when there is one (Fig. 360), 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. 167). 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. 167 (Calymene Blumen- 

 bachii), this suture terminates near the posterior outer angle. The glabella may have a 

 plane surface, or be more or less deeply transversely furrowed (Fig. 167), and usually 

 with only three pairs of furrows. 



Worms. — Worms are divided into Annelids and Helminths. 



The Annelids include, 1, the Chwtopods, having setas for locomotion; 2, the Sipuncu- 

 loids. having the body smooth and cylindrical; 3, the Bdelloids, or Leeches; besides 

 the two groups of free -swimming oceanic species, called Cheetognaihs (Sagittal), and 

 Gymnocopa (Tomopteris). 



The Chsetopods embrace the groups — 



(1.) Dorsibranchs, or free sea worms, having in general short branchial appendages 

 along the back. Many swim free in the open sea, and others live in the sands of sea- 

 shores or the muddy bottom. The Arenicola family includes species that burrow in 

 the sands of sea-shores. Fig. 160 represents the A. manna, or Lob-worm, which is 

 common on European and American shores, and grows to the size of the finger. One 

 species of Eunice has a length of four feet. 



(2.) The Tubicola, or Serpula tribe, which live in a calcareous or membranous tube, 

 and have a delicate branchial flower, often of great beauty, near the head. They are 

 confined to salt water. The tubes often penetrate corals, and the branchial flower 

 comes out as a rival of the coral polyps around it. 



(3.) The Terricnla (Oligochasta), or Earth worm tribe, destitute of branchial appen- 

 dages; as the common Earth-worm. 



Besides these, there are the Helminths, including various Intestinal worms, and the 

 Turbellaria. 



III. MOLLUSKS. 



The three grand divisions of Mollusks are — 



I. Ordinary Mollusks, having usually regular gills or branchice, 

 in addition to an outer enveloping fold of the skin called a pallium, 

 from the Latin for cloak ; as the oyster, snail, and cuttle-fish. 



II. Ascidian Mollusks. Unlike Ordinary Mollusks in being 



