114 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Larval Stages. 



In order to obtain the larval stages of Glyphioceras inci- 

 suni, a number of adults were selected, so as to make sure 

 of the identity, and the outer coils were broken off until the 

 desired size was obtained. This necessitated the destruc- 

 tion of several specimens, but was well worth while in view 

 of reliability of the results. The specimens were studied in 

 three different mountings, dry on card-board, in a drop of 

 water on card-board, and in water in a watch-glass over a 

 strong condensing lens. In the first way the surface mark- 

 ings are seen best, in the second the sutures and form, in 

 the third the internal structure when the specimen is trans- 

 lucent. The nomenclature used is that of Hyatt, published 

 in "Phylogeny of an Acquired Characteristic."' 



Phylembryonic . The protoconch represents the first shell 

 secreted by the shell-gland, and must have been formed 

 while the animal was in the ^g2,. It is quite possible that 

 some of the chambers were formed before the ^^o^ was 

 hatched, but this cannot be determined on fossils. The 

 protoconch is taken for convenience to represent the phy- 

 lembr3^onic stage of growth, the end of the embryonic, when 

 the class or phylum can be determined, and the animal is 

 already a cephalopod. In shape, the protoconch is a smooth, 

 rather elongate, bobbin-shaped, oval body, of which the 

 upper part projects forward in a lap, where the first cham- 

 ber was joined to it. The protoconch was not the whole of 

 the embryo chamber, for a part of the spiral tube must have 

 furnished a lodging for the embryo ; but after the formation 

 of the first air-chamber it is no longer possible to determine 

 how long the primitive body-chamber was. The protoconch 

 corresponds to the primitive nautilian shell from which the 

 ammonoids descended, but the parallelism is not exact, for 

 the initial chamber of the nautiloids is not calcareous, while 

 acceleration of development has pushed back to the embryo 

 the calcareous shell of the ammonoids. 



In the protoconch is seen the beginning of the siphon, or 



iProc. Am. Phil. Soc, Vol. XXXII, No. 143. 



