INVERTEBRATE PALAEONTOLOGY. ;',<),-, 



provided with broad, undefined, obliquely -transverse ridges, or undulations, 

 thai arch parallel t<> the obscure lines of growth, and become nearly or quite 

 obsolete as they approach the siphonal side, on which they are rarely repre- 

 sented by very small, irregular ridges, scarcely distinct from the marks of 

 growth. 



Septa moderately closely arranged, or sometimes a little crowded; 

 siphonal lobe nearly twice as wide as long, and provided with two large 

 terminal, widely separated, more or less spreading branches, each of which 

 has sometimes three, and sometimes two, nearly equal, digitate branchlets at 

 the end, and two or three similar lateral ones on the outer side; first lateral 

 sinus about as wide as long, but narrower than the siphonal lobe, and divided 

 at the free end into two short, nearly equal branches, each of which is again 

 less deeply subdivided into about two to three or four sinuous, spreading and 

 digitate branchlets ; first lateral lobe oblong-ovate, being longer and narrower 

 than the siphonal lobe, and deeply divided at its vnd into two very nearly 

 equal branches, with each from four to five spreading and digitate subdi- 

 visions, in part generally so arranged as to give the main branches a tripartite 

 appearance at their extremities; second lateral sinus of nearly the same size 

 as the first, and, excepting in unimportant details, similarly branched and 

 subdivided ; second lateral lobe broader and shorter than the first, and bear- 

 ing two large, equal, tripartite, sinuous, and digitate terminal branches, and 

 small digitate and simple lateral branchlets; third lateral sinus much smaller 

 than either of the others, with two unequal, short, sinuous, and dentate ter- 

 minal divisions, and a few irregular, short, smaller lateral spurs; dorsal or 

 antisiphonal lobe (ventral lobe of d'Orbigny and others) scarcely as large as 

 one of the terminal branches of the siphonal lobe, longer than wide, with 

 three or four small lateral branches, and normally a trifid free extremity.* 



No specimens of this shell, so tar as I am informed, have yet been 

 found in a condition to give exact measurements of an entire example. 

 Fragments, however, are not uncommon, measuring about two and a half 

 inches in their greater diameter by about two inches in their smaller, near 

 the aperture ; and one septate fragment before me measures 3. GO inches by 

 3.10 inches in diameter. From the average taper of numerous fragments, it 

 is probable that the length of large unbroken individuals maybe nearly three 

 feet. 



This species varies more or less in convexity and general form, as well 



* This lobe, in the particular septum figured on plate W, is abnormally bifid at the end. 



