210 PALEONTOLOGY OF NEW-YORK. 
Fig. 2 e. Transverse section of the specimen 2 a, showing the proportional diameters of the two, and 
the section of a still smaller tube within 2 a. 
Tn this instance, the specimen does not reveal enough to show whether the internal tubes 
are embraced within a siphuncle or not : the outer one is clearly marked with septa upon 
the outside, similar to the one within it; but of the interior one we know nothing. The first 
internal tube is clearly not a cast within the outer tube; for it preserves a shell with surface 
markings, as well as septa externally. This figure is given to show the similarity, general 
form and surface markings, both in the septate and non-septate tubes, which belong ap- 
parently to the same species. 
275. 7 ENDOCERAS PROTEIFORME, var. TENUITEXTUM. 
Pu. XLV. Figs.2a6, 3a6,& 5ab6c; and Pu. XLVIII. Fig. 2abc. 
This variety does not differ in form from the preceding. The longitudinal and transverse 
striz are more distinctly elevated and threadlike, being of nearly equal size in both direc- 
tions, giving the surface a texturate or weblike appearance. These striz are sometimes 
distinctly visible to the naked eye, while in other specimens they can only be distinguished 
by the magnifier. The septa are distant a little less than one fifth the diameter of the tube ; 
section circular ; siphuncle excentric. 
In some specimens of the last variety, the striae become more distinctly developed, and 
gradually assume the decided characters of such specimens as are described in the following 
figures. 
PLATE XLV. 
Fig. 2a. A fragment of a tube destitute of septa, presenting strong transverse and longitudinal strie. 
Fig. 2b. A portion of the surface enlarged. 
Fig. 3 a. A specimen with finer striae, showing the marks of septa. 
Fig. 3 6. A portion of the surface enlarged. The specimen 3 a@ diminishes more rapidly towards the 
apex than the preceding one, and the cancellation of the surface is finer. 
Fig. 5 a. This specimen presents a double tube or sheath, the outer one (or embryo tube) being entirely 
smooth, while the inner one, which is but little smaller, is marked by longitudinal and 
transverse strize as in the preceding figures. 
Fig. 5 b. A portion of the same enlarged te show the strie. 
Fig. 5 c. A section of the same, showing no septa or siphuncle. 
Pruate XLVIIL 
Fig. 2. An embryo tube, containing a young specimen of this variety. It has been broken at a 6 c, and 
presents the sections @ bc at the bottom of the plate, showing the septa and excentric si- 
phuncle, The surface marking of this young shel] is precisely like fig.3 a 4, Pl. xlv. 
