82 BULLETIN OF THE 



however, that the lines " X " delineated in the interior of the specimen 

 of Deroceras planicosta, Plate I, Fig. 6, show the junction of the 

 first septum with the dorsal side of the whorl. They are in the proper 

 position with relation to the external suture, and it is difficult to imagine 

 any other structure to which they could belong. I failed to find any- 

 thing similar in other specimens, and the original was accidentally lost 

 after the figure had been drawn, while transferring it from one glass 

 slide to another. 



The huge size and depth of the abdominal cells of the first septum 

 has no exact parallel, so far as I am aware, in any known adult 

 Cephalopod. The pouch-shaped lateral lobes also appear to be 

 peculiar. The sutures, however, vary considerably in the young of 

 the same species. In some specimens inferior lateral cells* appear on 

 the sides, and the lateral lobes are not so high, the abdominal cell, also, 

 varying proportionally in breadth and depth. These lateral cells, how- 

 ever, do not exceed the strict Nautilian limits, and remind the observer 

 of the slight inferior lateral cells of Nautilus Pompilius, both in position 

 and in outline. Often, however, they occur so exactly on the edge of 

 the embryonal umbilicus, and the descent into the lateral lobes is so 

 abrupt that the observer confounds the suture with the projecting edge 

 of the first whorl.f When such a specimen is viewed from the side by 

 transmitted light, and the ovisac is transparent, as it frequently is, the 

 shell appears to be pointed as in Nautilus, and the ovisac absent. 

 When, however, a few specimens are completely broken down, and 

 the ovisac and first septum laid bare, the error is easily corrected. 



In section, the first septum appears to blend with the wall of the si- 

 phonal coecum.t The enclosed transparent spaces, however, as indicated 

 at 1 e, 2 e, Plate II, Fig. 1, between the siphonal wall and the inner 

 side of the shell proper, probably represent all of this septum which ob- 

 tains along the median line. In other specimens which I have studied 

 this cannot be so plainly made out, and I should still be in doubt if 

 these transparent spaces had not been enclosed by the lining layer of 

 the shell. They can be compared in other respects also with the suc- 

 ceeding septa, which they resemble in position, size, and the peculiar 

 spreading or fan-shaped sections of the sutural portions or junctions. 

 The texture of the septum seems to be very distinct, but the drawing 



* Plate I, Figs. 2, 5. J Plate II, Fig. 1, 1 e. 



t Plate II, Fig. 7. Plate I, Fig. 4. 



