C. E. Beecher — Development of Shell in Tomoceras. 71 



described) until the volume is decreased to 40 cm 3 . The color 

 of free iodine is to be bleached by cautious additions of sul- 

 phurous acid (corresponding roughly to centinormal iodine) 

 and instantly diluted with water and neutralized with potassium 

 carbonate, the neutral carbonate at the first and afterward the 

 acid carbonate. The whole is to be cooled and titrated as usual 

 with iodine, using starch as an indicator. Its advantage is in 

 the rapidity with which it may be executed, the whole opera- 

 tion being easily completed in a half-hour. 



Art. VIII. — On the Development of the Shell in the genus 

 Tomoceras Hyatt ; by Charles E. Beecher, Ph.D. 

 (With Plate I). 



The leading embryonal characters of the genus Tomoceras 

 have been drawn mainly from results obtained in the study of 

 Tomoceras retrorsum, von Buch, and allied species from the 

 Devonian of Germany.* Probably the best study of any one 

 of the species is that given by W. Branco of T. retrorsum, var. 

 typum, Sandberger.f The adult features have been deter- 

 mined from the type T. {Gon.) uniangidare Conrad, and 

 other closely related forms. Hitherto our knowledge of 

 this species has not been sufficient to give a reasonably full 

 diagnosis of the genus in its developmental relations, and 

 the results of the following study aim to supply the deficiency. 

 The importance of this is evident, as the characters of the 

 type are of prime consequence, and because T. retrorsum 

 offers some differences in its development, and apparently 

 belongs to 07ie of the more advanced phases in the evolution 

 of the generic stock. Instead of presenting a gradual growth 

 from its simple nautiliform protoconch through several slightly 

 diverging stages, it exhibits, to a degree, the principle of 

 accelerated development, as will be shown hereafter ; while 

 T. uniangulare has a more uniform and complete growth, and 

 is probably one of the initial and most primitive species of 

 the genus. 



Besides the sutural and tubular development, the material 

 studied illustrates the inception and growth of the surface 

 ornaments, and as these features are rarely found, the princi- 

 ples involved are of more than generic application. 



* Proceedings Boston Society Natural History, vol. xxii, Hyatt: Genera of 

 Fossil Cephalopods, p. 320, 1883. 



\ Palasontographica, t. 27. Beitrage zur Entwickelungsgeschichte der fossilen 

 Cephalopoden, 1880. 



