94 THE NAUTILUS. 



differs in the truncated and much split-up cardinal teetl) and the 

 broadly rounded posterior end of the shell. The conipressus of Heude 

 will therefore be called I^odularia suhpressa Heude. 

 ( To be continued.^ 



THE DISCHARGE OF THE GLOCHIDIA IN THE UNIONIDa:. 



BY DR. A. E. ORTMANN. 



Only Lea has published a few facts which bear upon the question 

 of how the glochidia of the Unionidse, contained in the marsupium, 

 are set free (Observ., II, x), but some of his observations are entirely 

 wrong. Further, Simpson (Pr. U. S. Mus. 22, '00, p. 616) believes 

 that the "ovisacs" (which I call now placentulaj) of the genus 

 Strophitus are discharged through the walls of the gills, which 

 again is wrong. 



According to my observations the glochidia are discharged in the 

 natural way in the following species: Quadrula subrotunda (Lea), 

 Quadrida imdulata (Barn.), Pleiirohema coccineiim (Conr.), Plcuro- 

 benia eesopus (Greeny, Strophitus edeniulus (Say), Syniphynota costata 

 (Raf.), Anodontoides ferussacianus (Lea), Anodonta imbecillis Say. 



This natural way is: they go from the water-tubes (ovisacs), inside 

 of which they develop, into the suprabranchial canal, from this into 

 the cloacal chamber, and thence go out of the soft parts and the shell' 

 by way of tlie anal opening. 



In Quadrula subrotunda, Pleurohema coccineum and aesopus, the 

 whole placentte are discharged. In Strophitus edeniulus the whole 

 placentuln? are discharged, but sometimes the glochidia become free 

 already in the supnibranchial canal. In the other four species named 

 the glochidia are rather loose when discharged, and are issued in the 

 form of irregular musses, which do not stick together, so as to pre- 

 serve the shape of the placentas. 



Entirely different from these shells, which belong to the two sub- 

 families of the Uuionidce and Atioduntiuce, is the discharge in the 

 Lampsilince. Here the glochidia do not go out by the natural chan- 

 nels, but break through the walls of the gills, at the edge of the mar- 

 supium, by small holes formed for this pur|)ose, which close again 

 after the discharge. Each ovit^ac (water-tube) has one hole at its 

 distal end, and the glochidia are genei-Mlly discharged in irregular 

 masses, rather loosely connected, without preserving the shape of the 



