72 



Guide to the Invertelrata, 



Table 

 oases 

 80-85 



GALLEBY persistent types which possess enormous powers of multiplication, 

 East Side ^^ ^^^* entire beds of rocks may be said to be composed of their 

 Wall-cases naicroscopic shelly coverings. The living species are known also 

 12-14, to possess exceptional powers of endurance, and have special pro- 

 vision for the preservation of their lives in periods of drought; 

 the eggs retaining their vitality in a dormant state for years. 



Eepresentatives of these, as Leper ditia, Beyricliia, Bairdia, 

 Aristozoe, Carbonia, Candona, Cypridea, Cythere, Cypris, Frimitia, 

 and many others, may be seen in the table- and wall-cases; they 

 occur in rocks of nearly every age. 



2. — CoPEPODA. In the order Copepoda are placed numerous small 

 crustaceans, met with in incredible numbers both in fresh and salt 

 water. The fresh- water Cyclops (Fig. 120, 3), for example, is very 

 abundant in ponds and rain-water tanks ; and the Cetochilus (Fig. 

 120, If), although so minute, colours the sea with a reddish hue 

 for miles, and furnishes by its vast numbers abundant food for so 

 large a mammal as the ''right whale." They have not been 

 detected fossil in any of the rocks. In the Cladoceba the head 

 and antennce project, but the rest of the body is entirely enclosed 

 within a bivalved carapace ; the antennae are large and branching, 

 and serve as swimming-organs. Daphnia pulex (Fig. 120, i), "the 

 fresh- water flea," is a good example. It occurs in vast numbers 

 in fresh- water ponds, but is not known in a fossil state. 



3. — The Phtllopoda are Entomostracous Crustaceans having 

 a shell composed of two valves in which the body is more or less 

 completely enclosed, or it may form a buckler-like shield over 

 the forepart of the animal. The gills are attached to the feet. 

 Those living at the present day are found inhabiting both fresh 

 water and the sea, and are of small size. Protoearis Marshii 

 occurs in the Lower Cambrian of North America, and resembles the 

 modern Lepidurus and Apus (Fig. 121, 3, If). The living Brauchipus 

 (Fig. 121, 5), or Cheirocephalus, and Artemia are unprotected by 

 any shelly covering ; but a fossil Branchipus, named Branchipodites 

 vectensis, has been discovered in the Eocene of the Isle of Wight 

 (Table-case 85). Species of the genus Estheria are met with 

 in the Devonian and Carboniferous, and in all the subsequent 

 formations even to the recent seas where it is now living. 



4. — The order Phyllocaeida was founded to include the living 

 genus Nehalia (see Fig. 121, 2), with certain extinct forms believed 

 to be related to it, and which are considered to occupy an 



