86 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



incrusting (No. 3), and have a limy covering so as to be 

 quite hard and brittle ; some of the colonies form net- 

 works extending for many square inches over the surfaces 

 of stones and the blades of the great brown oar-weed. 

 Flustra, the " sea mat " (No. 1), is frequently found cast 

 up amongst sea-weeds. A small piece is shown magnified 

 at 2. Bugula (No. 4) is usually obtained by dredging ; 

 part of the colony alive and expanded with polypites and 

 "birds-head" processes is shown at 5. Forms like 

 Lepralia (3) are found under stones and on shells in rock 

 pools. Specimens of these and other kinds of Polyzoa are 

 generally to be seen in our tanks at the Aquarium. The 

 reports in our " Fauna " are by Miss L. R. Thornely. 



CRUSTACEA. 



(Figs. XII. to XVIII.) 



Crustaceans are animals such as crabs and lobsters, 

 shrimps and prawns, sand-hoppers and barnacles, and 

 innumerable smaller forms, " water-fleas " and the like, 

 which abound in almost all parts of our seas. They all 

 have segmented bodies and jointed legs, and a hard shell 

 or covering to the body. They are, then, " shell-fish " of 

 a kind, but they differ from the true shell-fish, such as 

 oysters and periwinkles, in having segments and legs. 

 Once the difference has been pointed out, no one can 

 mistake a shrimp-like shell-fish for a cockle-like shell- 

 fish. The former are Crustaceans and the latter Molluscs. 

 It is better to reserve the term shell-fish for the Molluscs. 

 Among the most abundant of lower Crustaceans are the 

 rock-barnacles or acorn shells (Balanus) which are so 



