THE NAIADES OF MISSOURI 127 



3. Proptera-Lampsilis-Group . In this division the best 

 adaptation for the proper respiration of the embryos is secured 

 by situating the numerous, dilated ovisacs in a more or less kidney- 

 shaped marsupium near to the branchial opening where the 

 postero-ventral margin of the mantle is set with papillae, flaps, 

 etc. The first members of this group have this mantle edge only 

 slightly crenulate and lamellate, while beyond the genus. Pro- 

 tera, is the culmination of the modern structure in the arrange- 

 ment of the inner edge with papillae or flaps close to, or remote 

 from, the outer edge. This group is represented by about thirty 

 species in this State. 



It may be added that the Lampsilinae are dissimilar to the 

 Unioninae in their breeding season in that practically- all the 

 species are long period breeders (bradytictic) , but that the glochi- 

 dia of these two sub-families are similar in form and in being spine- 

 less. It is especially to be noted that the members of these two 

 sub-families have developed perfect hinges in the adult shell, 

 whereas those of Anodontinae possessing glochidia with spines 

 have defective hinges. We should also note that the Lampsilinae 

 are able to spread their valves far apart — a habit which may 

 have some relation to the difi'erentiation of their mantle margins 

 in admitting greater incurrents of water — while the Unioninae 

 and Anodontinae show a primitive character in being unable to 

 force their valves far apart and accordingly in not developing 

 stronger papillae and more extended mantle edges at their siphonal 

 openings — ^a defect that may be somewhat counterbalanced by 

 the delvelopment of larger palpi than is very often seen in the 

 Lampsilinae. It may be stated further that there is not such 

 intergradation of forms in this sub-family as seen among the 

 Unioninae, or even as noticed among the Anodontinae as there 

 seems to be more distinctness and fixity of characters among the 

 several genera, especially as seen in the marsupial structures 

 upon which a good key is built. 



Genus Ellipsaria Rafinesque. 



1820 — Ellipsaria Rafinesque, Monog. Biv. Shells of R. Ohio., Ann. 



Gen. Sci. Phys. 

 1900b — Ptychohranchus Simpson, Proc. Ac. N. Sci. Phila., p. 79. 



'^Type, Ellipsaria fasciolaris Rafinesque 1 820 = phaseolus 

 Hildreth, 1828). 



