UPPER TRIASSIO SPECIES 115 



from such specimens as those represented by our figs. 10, 10 a, and 10 & on 

 pkte 10; my impression at that time being that the pecuhar forms, such as 

 that illustrated by figs. 5 and 5 a of plate 1 1 , belong to an allied but dis- 

 tinct species, differing in the development of lateral nodes, the flattening of 

 the peripher}^, and the singular elliptic or scaphitoid general outline in the 

 adult. For this form I had proposed the specific name scaphitoides {Gymnot. 

 scaphitoides, as the nomenclature here adopted would require). I had noticed, 

 however, the similarity of its inner volutions to those of G. Blakei, and had 

 considered the question of its possible identity with that species. But the 

 fact that there are some ten or eleven specimens in the collection, all 

 showing the form and flattened periphery seen in fig. 5, plate 11, while 

 none of those that I referred to G. Blakei, even of equal size (as that from 

 'which were drawn figs. 10 and 10 a on plate 10), show any traces of the 

 lateral nodes, flattening of the periphery, or elliptic general outline, I was 

 led to think the former could hardly belong to G. Blakei. 



Professor Hyatt, however, after studying the specimens carefully, 

 arrived at the concl'usion that these scaphitoid specimens with lateral nodes 

 and flattened periphery only represent a more advanced stage in the develop- 

 ment of G. Blakei. Consequently, I now yield my opinion to his greater 

 experience and advantages in tracing the different phases of development in 

 this order of shells, and adopt his conclusion. I prefer, however, to allow 

 my description of G. Blakei to stand as originally written, and to quote 

 below Professor Hyatt's remarks rather than rewrite my own. 



The following are Professor Hyatt's notes on G. Blakei, and its varia- 

 tions and development: 



" This species is smooth for the first three or four volutions. Then the 

 pilse begin to appear as lateral folds. During the next volution, the abdo- 

 men is smooth and broad; the whole form and mode of involution resemblinar 

 Lytoceras finibriatum. After this, a low, broad keel arises [see fig. 10 a, pi. 10], 

 and the increase in bulk is exceedingly rapid. Intermediate pilse [costse] 

 are added by folds of the shell near the abdomen on the sixth or seventh 

 volution [see fig. 10, pi. 10]. These soon coalesce with the longer pilse, and 

 form more or less prominent and subsequently a tubercular junction. On 

 the eighth or ninth whorl, the broad keel disappears, and the pilse are wholly 



