98 BULLETIN OF THE 



or breaking the continuity of the suture of the first septum on the ab- 

 domen. The prolongation into the ovisac was not discernible on the 

 abdomen, except in one specimen, and from the side not so distinct 

 as in Goniatites.* The figures of this portion, owing partly to the great 

 thickness of the specimen, and to its more attenuated structure, were 

 completed with great difficulty, and only after repeated observations. 

 By the use of dark ground illuminations and a powerful condenser, the 

 coccum extending below the first septum was seen from the abdominal 

 side in Fig. 5, Plate I, though the walls seemed broken and partly de- 

 stroyed ; the cone, however, Was not made out. Longitudinal sections 

 of several specimens gave substantially the same results as the single 

 one figured. The coecum is formed as in Goniatites by the siplional 

 funnel of the first septum, but the conical prolongation does not open 

 into the ccecum,t and its interior is filled cither with a succession of 

 other cones, or by a number of pillars stretching across its interior. The 

 peculiar aspect of this portion in the specimens examined has suggested 

 an explanation of this remarkable modification. When the first septum 

 was formed, it may have been composed entirely of the thin membra- 

 neous layer on the ventral side of the coecum, and the first thick layer at 

 y in the figure ; as the siplional sheath was built up or thickened, it was 

 carried forward on the ventral side, the different successive layers or 

 partial septa from y upwards, marking the resting-places in this transit 

 until at 1 e the first septum was completed. Whether this be so or not, 

 the conical part of the coccum has not, as far as my observations go, 

 any decided connection with the coecum when closely examined in 

 section, though when seen from the side, as in Plate I, Figs. 3, 4, a 

 connection appeared probable. 



Von Buch pointed out the anterior direction of the so-called siplional 

 funnel of Ammonites, and has been followed by all authors since his 

 time. The use of the microscope, however, readily detects here a very 

 curious error. The anterior siplional funnel of Ammonites is not iden- 

 tical with the true funnel of Goniatites and Nautilus, but an additional 

 organ. { In the adult nearly the whole thickness of the septum bends 

 in an anterior direction, reversing the shape of the lips of the funnel.§ 

 In the }<nnig, only a small part of the septum bends anteriorly, and the 

 funnel is partially maintained, while in the very youngest stages no such 



* Pie, I, Figs 3,4. t Hate n, Fig. 4, 



i [Mate II. n- 1 v. § Plato II. Fig. 5. 



