TIIK NACTII.fS. 95 



pl;iren(fp. Only in one Ci»j=e, Ptychobranchus, tl;e plactnla; are dis- 

 clmr^ied wliole. 



Tluonjili llic>e liole.s, of cour>e, llic plodiidia arc fniptird into (lie 

 brancliial cliainlier, and from this tlity mu.-t go out tlirou<'li tlie 

 biuncliial o|tt ning. 



I iiave diifctly observed this discharge tlirough the edge of the 

 marsnpiuni in tlie following species: rtychubrauchus phaseohis 

 (Ilil.ir.) (sjifcinuMi preserved in alcohol in liie act of discharging), 

 Laiti/'silis /uteolu (Lam.), LinnpsHis reutricosa (Uarn.), and Lamp- 

 silis inultiradiuta (Lea) (>f'en in life). 



I have seen evi.lence of this discharge, in tlie shape of openings at 

 the edge of ilie marsupinm, in alcoholic material of Lampsilis Inteola 

 (Lam.), Liniipsi'lt's viuUirudintu (Lea), /.(impsi/is nitsnta (Sav), 

 Propfera a/aiu (Say), R yracilis (Uarn.), and Obovarki circidus 

 (L.-a). 



It is very likely that the peculiar morphological structure of the 

 marsupinm of the Lav>psilinse is d.rectly connected with and due to 

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

 able to correlate the chit-f mor|)hol<>gical diH'erentiation of the Lamp- 

 sWvCE with a physiological ditlereiitiation. In the other two sub- 

 families, UniunUlos and Anodontince, the primitive and natural v/ay 

 of discharge has been preserved. 



But also between these latter two subfamilies we have morpho- 

 logical differences which are connected nith physiological dif^'erenti- 

 lion: the Uiiionidce possess the more primitive structure of the mar- 

 supinm, 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 AnodontincB we observe highly complex structures of the n)ar- 

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

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

 glochidia, 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 marsupiurn 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 



