THE NAUTILUS. 95 



placenta^. Only in one case, Ptycltobranchus, the placentae are dis- 

 charged whole. 



Through these holes, of course, the glochidia are emptied into the 

 branchial chamber, and from this they must go out through the 

 branchial opening. 



I have directly observed this discharge through the edge of the 

 marsupium in the following species: Ptycliobranchus p/taseohis 

 (Hildr.) (specimen preserved in alcohol in the act of discharging), 

 Lampsilis luteola (Lam.), Lampsilis rentricosa (Barn.), and Lamp- 

 silis multiradiata (Lea) (st j en in life). 



I have seen evidence of this discharge, in the shape of openings at 



the edge of the marsupium, in alcoholic material of Lampsilis luteola 

 (Lam.), Lampsilis multiradiata (Lea), .Lampsilis nasuta (Say), 

 Proptera alata (Say), P. yracilis (Barn.), and Obovaria circulus 

 (Lea). 



It is very likely that the peculiar morphological structure of the 

 marsupium of the Lampsilinse is directly connected with and due to 

 this " unnatural " discharge of the glocliidia, and thus we would be 

 able to correlate the chief morphological differentiation of the Lamp- 

 sil'nKZ with a physiological differentiation. In the other two sub- 

 families, Unionidce and Anodontlncs, the primitive and natural way 

 of discharge has been preserved. 



But also between these latter two subfamilies we have morpho- 

 logical differences which are connected with physiological diff'erfnti- 

 tion : the Unionidce possess the more primitive structure of the mar- 

 supium, and they are all "summer breeders," or, to express the 

 characteristic feature, are forms with a short breeding season. The 

 glochidia are here discharged as soon as they are fully developed. 

 In the Anodontince we observe highly complex structures of the mar- 

 supium, which apparently are correlated with the fact that they are 

 " winter breeders," or forms with a long breeding season. Here the 

 glocliidia, after being fully developed, are not immediately dis- 

 charged, but are carried through the winter, and for this purpose 

 special structures are present which serve for the proper aeration of 

 the marsupium during this period. 



I publish these observations and conclusions chiefly with a view to 

 induce others to test them by looking for additional cases in other 

 species and genera. 



NOTES ON CALIFORNIA SHELLS. 



BY W. II. DALL. 



During the past summer I visited the Pacific coast with the object 

 of gathering data on the tertiary and recent mollusk faunas of the 



