SPIRTFERA. 221 



From this list it will be seen that not more than about twenty-three or four species 

 of Spirifera have been satisfactorily determined, 8. elliptica, 8. mesogonia, Sp.fusiformis, 

 Sp. Reedii, Sp. minima, and 8. subconica, 8. mosquensis, C. dorsata being probably to 

 some extent synonyms or varieties, and not sufficiently studied from want of sufficient 

 material. I will now add a few remarks with reference to some of the species. 



Spirifera striata, Martin (p. 19). Plate II, figs. 12 — 21, and figs. 9 — 11. Referred to 

 8. duplicicosta, and probably the young of 8. striata; Plate III, figs. 2 — 6, and 

 Plate LII, figs. 1, 2. 



This is a very variable species, the shell is generally transverse, but sometimes it is longer 

 than wide ; and I am therefore not quite certain whether the specimens referred to Sp. Mos- 

 quensis do in reality belong to the Russian type. For instance, the specimen, PL LI, fig. 1, is 

 certainly 8p. striata, and it will remain a question for future determination whether the 

 specimens, PI. IV, figs. 13, 14 ; and PI. XIII, fig. 16, do really belong to 8p. Mosquensis. 

 Mr. J. Wright is of opinion that the so-termed Sp. clatharata, M'Coy (p. 21, PI. Ill, 

 fig. 6) should be considered a synonym of Sp. bisulcata rather than of Sp. striata (although 

 in 1855 so referred by Prof. M'Coy), for the description and figure in the ' Synopsis' agrees 

 very closely with some of the finely-ribbed varieties of Sp. bisulcata, and that shell M'Coy 

 describes in p. 120 of the last-named work, "with three or four ribs on the mesial 

 fold." It appears evident, likewise, that Sp. striata, as described in the ' Synopsis,' 

 includes both Sp. striata and the larger forms of Sp. bisulcata ; Sp. bisulcata of the same 

 author refers only to the young of that species. 



Spirifera duplicicosta, Phillips (p. 24). Plate III, figs. 3, 4, (?) 5 — 11. Plate V, figs. 

 35, 37, incorrectly referred to S. trigonalis, Plate LII, fig. 6. 



This very variable species is sometimes with difficulty, and even uncertainty, dis- 

 tinguishable from certain shapes of Sp. striata. Mr. Burrow is of opinion that 

 Sp. humerosa, Phillips, (p. 23 PL IV, figs. 15, 16), should be considered a thickened 

 ponderous local variation of 8. duplicicosta ; and although I was at one time disposed to 

 view it as distinct, am now more inclined to follow Mr. Burrow by placing it among the 

 varieties of the last-named species. The mesial fold in 8. duplicicosta is sometimes much 

 prolonged beyond the level of the lateral portions of the valves, as seen in PL V, fig. 35, 

 and PL LII, fig. 6 ; and it is even sometimes difficult to distinguish certain examples of 

 S. duplicicosta from S. striata. 



