REPRODUCTION AND ARTIFICIAL PROPAGATION OF FRESH-WATER MUSSELS. 14I 



LONG PERIOD OF GRAVIDITY. 



In the forms which fall into this category the eggs are fertiUzed, as has been stated, 

 during the latter half of the summer, from the middle of July to the middle of August, 

 and the glochidia, instead of being discharged when fully formed, are carried in the 

 marsupium until the following spring or early summer. In fact, in some cases the 

 close of one breeding period may overlap on the beginning of the next, as one may still 

 find in late July a few straggling females gravid with glochidia formed in the previous 

 autumn, while in other individuals of the species at the same time and in the same 

 locaHty the eggs are passing into the gills for the next season. This seems to be true 

 of several species of LampsUis. We have encountered it in ligamentina , Conner (1909) 

 records it for radiata and nasuta, while Ortmann (1909) states that his observations 

 make it probable for ventricosa and luteola. Yet, as Ortmann observes, it is generally 

 true that an interval exists between the close of one period and the beginning of the 

 next. This interval, however, varies in length in different species, in some extending 

 from late spring until August, whereas in others it is of much shorter duration. It is 

 also to be noted that the discharge of glochidia does not take place in all of the indi- 

 viduals of a species at the same time, but on the contrary, spawning may extend over 

 a considerable period throughout the spring and early summer (cf. Ortmann, op. cit.). 



All of the genera included in Simpson's Heterogenae, Ptychogens, Eschatigenae, 

 and Diagenae have the long period of gravidity, as do also a number of genera of the 

 Homogenge (Alasmidonta, Anodonta, Anodonioides, Arcidens, Symphynola), while the 

 Mesogense are represented in this group by Cyprogenia. These genera are embraced in 

 Ortmann's subfamiHes AnodontincB and Lampsilince, and it should be noticed that in 

 all the gills show a high degree of specialization in adaptation to the marsupial func- 

 tion, a specialization which is undoubtedly correlated with the habit of retaining the 

 glochidia over a period of several months. 



In the following list are given the species in which we have determined the long 

 period of gravidity : 



Alasmidonta truncata. Lampsilis ligamentina. 



Anodonta cataracta. L'ampsilis luteola. 



Anodonta grandis. Lampsilis recta. 



Anodonta implicata. Lampsilis stibrostrata. 



Arcidens confragosus. Lampsilis ventricosa. 



Cyprogenia irrorata. Obovaria ellipsis. 



Dromus dromus. Plagiola elegans. 



Lampsilis (Proptera) alata. Plagiola secnris. 



Lampsilis (Proptera) lasvissima. Strophitus edentulus. 



Lampsilis anodontoides. . Symphynota complanata. 



Lampsilis gracilis. Symphynota costata. 

 Lampsilis higginsii. 



Ortmann (1909) has published some observations on the breeding seasons of the 

 Unionidae of Pennsylvania, supplemented by data from Lea and Sterki; his results in 

 85079° — Bull. 30 — 12 10 



