56. 



pleuro-pedal connect i-ves are still separated for a part of tlrieir 

 ext ent . 



6. ¥it3^ the Nixculidae, th.e otooysts open freely to 

 tlie outside. 



One can. conclude frora this that the Solenomyidae are 

 less primitive tlian the Nuculidae, and that the Lar.elli'brai'iclis 

 actually the most archaic are represented^ by the latter family and 

 spec i all 7/ by Nucul a . " 



In this, reference is made directly to Yoldia only in 

 number 2, aiid the statement here made does not hold good. The 

 foot muscles of Yoldia are surely among the most highly developed 

 of any to be found in the Lamellibranchia, ai^d the only reason 

 they occupy so much of the dorsal margin is because of their 

 enormous size. Numbers 3 and 6, -which refer to t}ie Nuculidae 



in general, do not seem to hold good with this species. 



EMBRYOLOGY. 



The most striking peculiarities in tlie development of 

 Yoldia are connected with the formation and disappearance of the 

 test. 



I find similar tests in the embryos of two species of 

 ITucula (IT. proxiiia and N. delphonodonta) , in both* of "wfiiich cases 



