282 ORTMANN— CORRELATION OF SHAPE AND 



into this problem, which may necessitate some radical changes in our 

 Naiad-nomenclature. 



This much is certain, that F. pilaris, the representative form in 

 the upper Tennessee of F. suhrotunda from the Ohio, behaves 

 exactly as F. suhrotunda, but the headwaters-forms of the two, in 

 the upper Tennessee and the upper Ohio drainages, although very 

 similar, have no direct genetic connection, and undoubtedly have 

 developed independently of each other. 



Group of Fusconaia flava in the Upper Ohio-drainage. 



I classify the forms belonging here as follows. 



1. Fusconaia flava (Rafinesque). — Dia. less than 55 per cent. 

 Ohliquaria flava Rafinesque, '20 (trib. of Kentucky, Salt, Green R.). 



— Quadrula flava Vanatta, Pr. Ac. Philad., '15, p. 557. 

 Dia. (Conrad, '37) : 43 per cent.; (Vanatta) : 39 per cent, 

 Unio rubiginosus Lea, '29 (Ohio). — Quadrula ruhiginosa Simpson, 

 '14. P- 872. 

 Dia. (Lea) : 44 per cent.; (Simpson) : 41, 34, 53 per cent. 



2. Fusconaia flava trigona (Lea). — Dia. 55 per cent, and 

 over. 



Unio trigonus Lea, '31 (Ohio R., Cincinnati and Louisville). — 



Synonym to Quadrula undata (Barnes), according to Simpson, 



'14, p. 881. 



Dia. (Lea) : 63 per cent. 



Probably also U . iindatus Barnes, '23, belongs here. This form, 

 has been discussed by Walker (Nautil., 24, '10, p. 24), who says 

 that it is the same as trigomts. He gives the diameter of 68 per 

 cent. Simpson (1. c), who follows him, gives it as 60, 61, and 76 

 per cent. 



Walker and Simpson probably are right in regarding trigonus 

 and U7idatus as synonyms, as far as it concerns obesity. However, 

 I think that they difiter in the development of the beaks, iindatus 

 having higher beaks, so that the outline is more triangular, while it 

 is subtrapezoidal in trigonus. Of typical undatus I have no good 

 material, and this form is not found in the upper Ohio. Wliat 1 

 have from this region (vicinity of Pittsburgh and upwards) repre- 



