CHAP. X. BRANCHIOPODA OHELYOSOMA. %Q3 



the valuable Essays, &c. published in their own country on 

 the species, we have not ventured to carry our analysis 

 so far : our object for the last twenty-three years has 

 been to discover the fundamental principles of their 

 natural arrangement. How far we have done this, time 

 alone will show. Much uncertainty, indeed, hangs over 

 the location of one or two genera ; but this, however 

 desirable to be cleared up, affects not the principle itself, 

 for that coincides with all we know of the universal 

 laws of animal variation. 



(273.) Our remaining space is now so contracted, 

 that we can do no more than merely glance at the two 

 remaining tribes of the DITHYRA. The Branchiopoda, 

 indeed, have already been slightly noticed (238); while 

 the annexed cut (fig. 63.) of Mr. Broderip's CHELYOSOMA 



will give a good idea of this most extraordinary animal. 

 According to that very able naturalist, it adheres to 

 stones by coriacious processes from the lower part. It 

 must be observed, however, that on this lower or cup- 

 shaped part, there are slight traces of separation into 

 plates, but without internal muscular fibre. The upper 

 surface is flat, and consists of eight coriaceous, some- 

 what horny angular plates, which are so disposed that 

 the branchial orifice (a) is surrounded by three plates, 

 and the anal orifice (6) by four : each of the plates are 

 marked by elevated striae, as in the tortoises. The valves 

 of the orifices are opened and closed by muscles, adhering 

 at one end to the inner surface of the tunic (not of the 

 mantle), and on the other to a small papillary process on 

 u 3 



