172 THE PROCEEDINGS OF THE LINNEAN SOCIETY 



radiating or branched, generally parallel to the outer edge, and 

 extending two-thirds towards centre. Tubercles of both surfacei 

 arranged in oblique lines across the plates. There is only ona 

 species. 



Aeachnoides placenta. Linnaeus. Found at Cape Grenville 

 and Darnley Island, by the " Chevert." It is also known in New 

 Zealand, and is very common on sandy shores, within the tropics 

 of E. Australia, where it is found lightly covered with sand at 

 low water. 



Sub-Order 3. — Petalosticha, Haackel, 1866. 



Generally heart-shaped urchins without teeth. Ambulacral 

 system petaloid. Anal and apical system disconnected. In this 

 order we have certain narrow bands of fine milliaries which we 

 called Fascioles, which are visible as depressed lines when the 

 urchin is covered with spines, and which latter are of greatly 

 disproportionate size. The large bristle-like curved spines are 

 seated on the larger tubercles. The smaller ones frequently make 

 a coat-like fur. The fascioles are covered with small embryonic 

 spines which act as a sieve, and serve to keep particles of dirt 

 from the pores. They are either round the petals, (peripetalous) 

 anal, (round the anus) internal running along the grooved side 

 of the test which corresponds to the odd ambulacrum, and between 

 the end of the posterior petals and the apical system, or lateral 

 Petalosticha are further distinguished by the formation of 

 Plastrons : that is, a closely packed tubercular area of defined 

 outline between the mouth and the anus. Pores round the mouth 

 connected by furrows, forming elegant designs, to which the 

 name of phyllodes is given. These phyllodes are separated by 

 clusters or nobs of tubercles in the A. spaces called Bourrelets ; 

 the phyllodes and bourrelets form the Floscelle. 



The first family is Cassidulidse, which does not seem to be 

 represented in Australia. It is limited to species without plastrons 

 or fascioles. There is one species of Echinobrissus in New 

 Zealand. 



