GRAPTOLITES OF NEW YOUK. I'AHT t 697 



we had occasion to verify in our mateiial, in regai'd to Salter's figui'es, in com- 

 bination with other chai'acters, it must be concluded that Salter's first two 

 drawings and his description [1853, p.87] can apply only to the form later on- 

 described as D. gibbei'ulus by Nicholson. Of the two drawings com- 

 prised in a later publication [1863, p. 137, fig.l3a, 13b] under this name, the 

 former is surely the Didymogi-aptus, the latter represents probably a Tetra- 

 graptns bigsbyi. This conclusion is supporte dby the fact that a long 

 nema is noticeable in the first two drawin^-s and is also cited in the original 

 description ; for, while the species of D . g i b b e r u 1 u s are notable for their 

 long nema, one will not notice this filiform suspensory organ among hundreds 

 of specimens of T e t r a g r a p t u s bigsbyi. 



It is, hence, apparent that Saltei' had before him, at the time of the 

 original description of D . c a d u c ens, the form which, later on, was described 

 and is generally known as D . g i 1) b e r u 1 u s Nicholson, a name which has, 

 then, to give way to Salter's older name. Salter's specimens were obtained by 

 Dr Bigsby from the " Lauzon Precipice," and came therefore from the Quebec 

 shales. Hall had evidently no examples of this species in his material from 

 the Quebec shales, or he would not have failed clearly to recognize the differ- 

 ence between his Tetragraptus bigsbyi and D. cad nee us Salter. 

 He states in regard to the former ; " These fonns resemble the G r a p t o 1 i 

 thus caduceus of Salter which was obtained by Dr Bigsby from 'the 

 Lauzon Precipice,' and I have hesitated in regard to making of them a 

 new species." The writer has found D . (g i b b e r u 1 u s) c a d u c e u s in the 

 Deep kill shales, so that there can })e no doubt of the presence of that species 

 on this side of the Atlantic. 



R. Etheridge jr figures both fonns here discussed as Tetragraptus 

 b r y o n o i d e s, considering D. caduceus as a synonym of that species. 

 It is clear, however, from his description, that he Avas aware of the constancy 

 of the differences of the two fonns, united by him under that name, and lie 

 suggests that Salter's name might be retained as a varietal designation for 

 such forms as those shown by his figni-es 3 ;ind 4, which represent specimens 

 of D. gibberulus Nicholson. 



