148 DEVONIAN FAUNA. 
Orthis deformis, Hall, has much finer and closer ribs. 
Some forms of Streptorhynchus Chemungensis, Conrad,® sp., are considerably 
distorted, but their ornament seems finer and more even, though sometimes when 
the stria are in a double series the major striz give a very coarse appearance to | 
the surface.’ 
Whether it is more than a variety of O. wmbraculum seems doubtful, but until 
further evidence is collected there are hardly sufficient data for uniting it with 
Schlotheim’s shell. 
Davidson * has figured similarly distorted examples of Streptorhynchus creni- 
stria, Phillips, sp. 
Hall® remarks that the distortion of the ventral valve in the genus Derbyia is 
much greater than in that of Orthotetes, and species of that genus closely 
resemble the present shell. He regards this distortion as an evidence that the 
shell was attached when young. 
4. Genus.—Stropuomena, de Blainville, 1825. 
Hall,° in the last volume of his ‘Pal. N. Y.,’ has elaborately discussed the 
historic claims of the terms Strophomena, Leptena, &c., coming to the conclusion 
that Strophomena should be restricted to shells of the type of St. rugosa, 
Rafinesque (which is supposed to = Leptena planumbona, Hall) ; Leptena to shells 
of the type of St. rhomboidalis ; Rafinesquina, Hall, to shells of the type of L. alter- 
nata, Conrad ; and Plectambonites, Pander, to shells of the type of L. transversalis. 
These changes would cause much confusion among the multitudes of described 
species, as Davidson and Saller have been almost universally followed in taking 
St. rhomboidalis as the type-form of Strophomena, and L. transversalis as that of 
Leptena. It seems unadvisable to introduce such extensive changes unless the 
evidence is conclusive, and Hall’s evidence is certainly not more than presumptive. 
The whole question hangs on the meaning of the type-species “ St. rugosa, 
Rafinesque.”’ Rafinesque does not appear to have described his shell himself, and 
even the identity of the species primarily described under that name by de 
Blainville is shrouded in uncertainty. It is generally supposed to be L. planum- 
bona, Hall; but Hall himself mentions the important fact that specimens of Sé. 
rhomboidalis in Rafinesque’s own Collection bore the labels of Strophomena 
1 1859, Hall, ‘ Pal. N. Y.,’ vol. iii, p. 174, pl. x a, figs. 13 a, 6; and pl. xv, figs. 3a, b. 
2 1867, ibid., vol. iv, pt. 1, p. 67, pl. x, figs. 13—18. 
3 Ibid., figs. 4, 6. 
4 1859, Davidson, ‘ Brit. Foss. Brach.,’ vol. ii, p. 124, pl. xxvii, figs. 2, 5. 
5 1892, Hall, ‘Pal. N. Y.,’ vol. viii, pt. 1, p. 263. 6 Ibid, p. 245, 276, &e. 
