PLATE 50. 
Fig. 1, 2, 3. ENDOCERAS PROTEIFORME. (Pag. 213.) 
1 a, An embryo tube containing a young shell. This specimen is more elongated, and less rapidly attenuating 
than the prevailing forms of the species : the outer tube is smooth, while the inner one is striated. 
1b. This tube is more slender than the usual forms, but does not differ in other respects. 
2a,b. Fragments of smooth embryo tubes, apparently of the same species, differing only in being more 
suddenly contracted and aculeate near the apex. 
2c,d. Parts of the siphuncle separated from larger shells, still retaining the embryo tube within. The si- 
phuncle is marked by oblique or ascending annulations, indicating the junction of the septa; which 
direction of the annulations is due to the lateral or excentric position of the siphuncle. 
3. An embryo tube, more conical than any of the others. 
