CEPHALOPODA. 473 



GONIATITES OWENI, Var. PARALLELA. 

 PLATES LXXIII, FIGS. 1, 2; LXXIV, FIG. 10. 



Gimiutites Oweni, var. parotitic, Hall. Thirteenth Rep. State Cab. Nat. Hist., p. 101, figs. 13, 14. 1860. 

 •' " " " " Illustrations Devon. Fossils: Cephalopoda, pi. 73, figs. 1,2. 1876. 



The Goniatites Oweni, var. parallela, was indicated in the original description 

 of the species. 



The form and general proportions of this variety are not materially different 

 from the typical forms of the species, though the volutions are sometimes less 

 rotund. The umbilicus is always smaller, and the inner volutions a little more 

 covered. The sides of the dorsal lobe are quite parallel, and the extremities 

 reach beyond the arch of the saddle in the next posterior septum. This gives 

 an apparent continuity to the septa, and the ventrum is thus impressed with 

 two parallel continuous grooves limiting the margins of the ventral lobes. 

 This feature indicates a closer arrangement of the septa throughout — a feature 

 usually quite perceptible on the lateral faces of the volutions. 



In addition to these characteristics the tube is often, or usually, distinctly 

 constricted at somewhat regular intervals by shallow, transverse grooves, which 

 affect the smallest specimens, but which become more conspicuous in older ones, 

 as shown in figure 8 of plate 73. 



It is, however, by no means established that this constriction affects only 

 the var. parallela, for it is sometimes seen in the younger and more rotund forms 

 DOMettring the typical characteristics, while the septa are comparatively more 

 distant, the impressed lines on the ventrum are not continuous, and the ventral 

 lobe does not extend so far as the summit of the next posterior saddle. This 

 is true in some well-preserved forms of younger individuals, and it may be 

 a question whether the characters distinguishing the varietal form are not 

 acquired in the progress of growth. 



The two varieties of form occur in the same locality and position and without 

 marked difference in comparative numbers. 

 60 



