M. F. Plateau on the Freshwater Crustacea of Belgium. 367 



with fragments of it, whivjh they have undertaken to examine ; 

 and I hope one or more of them Avill publish the results of 

 their examination. 



The fish of which it forms a part is at present unknown 

 to naturalists ; and therefore the name of Myriosteon Higginsii 

 may be retained. 



Since the above was written, Prof. Kolliker and Dr. Giinther 

 have sent me a preparation of the specimen mounted as a slide 

 in Canada balsam ; and they have no doubt it is part of a 

 cartilaginous fish. They have now decided that it is one of 

 the three or five bony tubes which strengthen and support the 

 beak of the sawfish (Pristis), and thus confirm Mr. Carter's 

 account ; but how these tubes became so completely separated 

 from each other and from the other bones of the beak is diffi- 

 cult to imagine, and shows the great power of the sun in tro- 

 pical regions. 



British Museum, April 7, 1870. 



XLI. — Researches on the Freshwater Crustacea of Belgium. 

 (Second and Third Parts.) By Felix Plateau*. 



In the present day we have witnessed the appearance of many 

 works on the freshwater Crustacea. In England especially 

 we may cite the researches of Messrs. Baird, Lubbock, Brady, 

 Norman, &c., a portion of which have been published in this 

 journal. After these important memoirs and those relating to 

 the same subject which have appeared in Germany, Sweden, 

 and elsewhere, nothing remained for me, so to speak, but to 

 glean the details which have been neglected by preceding 

 earcinologists. 



Genus Daphnia. — It seemed to me that it would be useful 

 to make a complete study of the dermal skeleton of the Daph- 

 nia;^ which has hitherto been very imperfectly known ; I have 

 endeavoured to apply to it the methods of analysis of MM. 

 Milne-Edwards, Spence Bate, and others, and to compare it 

 as far as possible with the cutaneous envelope of the Deca- 

 poda. 



The body includes three parts — the head, thorax, and abdo- 

 men. The portion of the valves and of the test which covers 

 the apparent head answers to the carapace or scapular ring of 

 the higher Crustacea ; the cardiac region is represented by the 

 triangular piece which covers the heart, and the branchial 

 region by the valves. 



* M^m. de I'Acad. Roy. de Belgique, Mem. des Savants strangers, 

 tome XXXV. Abstract communicated by the Author. 



