TO JUNCTION OK (1IJAND AND GREEN RIVERS. 131 



not they agree witlitlio.se of the forms under consideration, though it is probable they 

 will be found to present essentially tlie same characters. It is, therefore, chiefly owing 

 to the probable identity of our specimens with those investigated by this distinguished 

 author (who doubtless had an opportunity to make direct comparisons witli authentic 

 European examples of Lanark's species) that those under examination are here 

 referred provisionally to l>. aiin-ps. 



As I have had an opportunity to examine but two authentic specimens of B. anceps 

 from foreign localities, and these were mere fragments, I have no means of knowing 

 to what extent that species varies in form and internal characters. It is worthy of 

 remark, however, that the two fragments of It. aiiccpK here alluded to, as well as tlie 

 figures of that species given by Professor Mronn in his Lethtsa Geognostica, and those 

 given by d'Orbigny in his Pu/roi/tohgie franc.ais, although agreeing very nearly in 

 form and surface-undulations, all differ from our New Mexican specimens, as well as 

 from those figured by Dr. Roemer, in being rather distinctly carinated on the dorsal side. 

 Again, on comparing the septa of the two European specimens of B. anceps mentioned 

 above with d'Orbigny's enlarged figure of the same, it was found that they agree quite 

 nearly in all their essential characters, while they both present rather marked differ- 

 ences from those of the New Mexican forms. 



These differences consist not merely in the greater obtuseness of all the smaller 

 divisions of tlie septa-lobes of the specimens under examination, but also in the form 

 and mode of branching of the lobes themselves, as may be seen by reference to the 

 figures given on plate II. I strongly suspect these differences to be of specific impor- 

 tance; but, without other means of comparison than those now available, it is difficult 

 to determine whether this is the case or not. 



It will be observed that the figures on plate II represent two rather marked varie- 

 ties, some of the specimens being more slender and less compressed than others, and 

 provided with obtuse, nearly circular, nodes, instead of transversely-elongated, arcuate 

 undulations, as in the more compressed forms. A careful study of the whole series of 

 specimens, however, shows that there are intermediate; gradations between these two 

 forms, while the septa present almost precisely the same characters throughout the 

 entire series. 



These two extremes of form bear very nearly the same relations to each other that 

 B. asper of Morton does to Iris B. carinatus, which forms they also very closely resem- 

 ble in their external characters, excepting that neither of them is ever carinated on the 

 dorsal side, as in the typical B. carinatus of Morton. Dr. Roemer suggests that the 

 latter is probably not distinct from B. anceps of Lamarck; and Mr. Gabb, who 

 examined Dr. Morton's typical specimens, has arrived at the conclusion that not only 

 that form (./>'. carht(tttis), but B. asper also, are merely' varieties of B. anceps* (See 

 Proceedings of the Academy of Natural Sciences of Philadelphia for November, 1861.) 

 Without expressing an}- decided opinion in regard to this latter conclusion (not 

 having seen the specimens upon which it is based), 1 would remark that the figures ot 

 the septa of B. car-hint nx and II. ax/in- given by Mr. Gabb, seem to present some rather 

 marked differences from those of B. aneeps, though it is not improbable that there may 



* Our figures 2 a and 2 b, on plate II, represent a section and a septum of B. anceps of Europe, for comparison. 



