ART. l-'3 FRESH-WATER MUSSELS, ANODONTITES MARSHALL 13 



may be pardoned for harboring doubt as to the correctness of his 

 discoveries. Should his observations be confirmed, the fact will 

 lessen our faith in analogy, and we may then doubt that the naiades 

 normally have taxodont hinge, and a number of other beliefs which 

 we accept as truth but which rest upon analogy and not upon abso- 

 lute proof will have to be discarded. 



Ihering seems to be the only naturalist who has seen the embryo 

 of Anodontites. Simpson never saw one, nor did Ortmann (1921, 

 p. 567), who says regarding the whole subfamily Mutelinae : "It 

 is a very singular circumstance that I have not been able to find 

 lasidia (or any other form of mature larvae) in my material, al- 

 though a good many gravid females of various species and genera 

 are at hand." I have been trying for a long time to obtain from 

 naturalists in Costa Rica, Colombia, British Guiana, Venezuela, and 

 Uruguay any species of naiad with a triangular sinulus containing 

 ripe embryos, but so fur without success. Attention is called to 

 this in (he hope that naturalists may be led to make special effort to 

 obtain material that will either confirm or disprove Ihering's re- 

 sults. Proof or dis]3roof vroukl be a great stride forward in our 

 understanding of the naiades. 



Notwithstanding the difiiculty of obtaining specimens of the 

 Mutelinae containing ripe embryos, it is known from the observe. - 

 tions of Ihering and Ortmann that the inner gills ,form the mar- 

 supium. Species belonging in that subfamily may be obtained from 

 Mexico to Patagonia and also in West Africa. Any species show- 

 ing the cliaracteristic nearly equilaterally triangular sinulu>3 or liga- 

 mental scar at the rear end of the ligament would probably give the 

 key to the embryology of the whole subfamily, provided it con- 

 tained ripe embryos. The breeding season is unknown ; hence it 

 might be necessary to look for gravid specimens each month in tlie 

 3'ear until the proper season is discovered. The inner gills when 

 gravid probably become padlike from the multitude of embryos 

 gorging them, while the outer gills remain normal. Ripe embryos 

 in the naiades whose embryology is known are minute white shells 

 consisting of two valves. A little of the inner gill of South Ameri- 

 can species teased out and examined under a microscope will re- 

 veal at once whether embryos are present. 



