128 



THE NAUTILUS, 



THE IDENTITY OF THE NAYAD-GENUS NODULAEIA C05BAD WITH 

 UNIO EETZITJS. 



BY DR. A. E. OBTMANX. 



The type of Conrad's genus Xodutoria (Proc. Ac. Philad. 

 6. 1S53, p. 266 ) is Unio douglasiae Griffith & Pidgeon. Simp- 

 son (Syn.. 1900.. p. S06, and Descr. Cat.. 1914, p. 949) has 

 associated, in this genus, a large number of species from Asia 

 and Africa, and places it in his subfamily Hyrian<r. to which 

 he assigns radial beak sculpture and a marsupiiun formed by 

 the inner gills only, the latter character resting upon the 

 observation of two species only. 



Already Haas (System. Conchyl. Cabinet, vol. 9. Heft 44. 

 1911. p. 65 ff.) has pointed out that this conception of Xodu- 

 laria cannot be maintained, since just the type-species ydoug- 

 l<isia() does not possess the characters assigned to the sub- 

 family by Simpson : its beak sculpture is essentially of the 

 zic-zac type, and its marsupiiun is formed by the outer gills. 

 His examination of this species ( and several others. L c. p. 

 67) has revealed several other differences from Simpson's 

 description of the anatomy of N. japanensis. and. as far as it 

 goes, we are to conclude that " Xephronuias d^ugl<isiae" is 

 not allied to the Hyriine type of Xayades, but rather to that 

 type represented by Unio Retzius (1788) in the restricted 

 sense as defined by myself (Ann. Carnegie Mus. 8. 1912. p. 

 273) : that is to say, it belongs to the family Union-icUr, sub- 

 family Unionin<r. This is clearly shown by the existence of a 

 supraanal opening separated from the anal ("Mantelschlitz 

 unten geschlossen " ), and by the marsupiiun. 



From the characters of the shell, chiefly the zic-zac beak 

 sculpture, it was to be inferred that U. douglosiae comes close 

 to the genus Unio (compare my key of genera. L c. pp. 239 

 and 240 ) ; but the chief character of Unio. the subtriangular. 

 hooked glochidium. has not been observed hitherto, the gravid 

 females investigated by Haas having only eggs, and not 

 glochidia. 



Recently Mr. B. Walker has been kind enough to send to 

 me the soft parts of two gravid females of U. douglosiae Griff. 



