44] 
mere spot, so that this must be regarded as doubtful. In the later 
paranepionic it is unquestionably propioventran or subventran. In 
the neanic stage it approximates to and attains an extracentroven- 
tran position, which it retains throughout life. The position in the 
gerontic stage was, however, not observed. 
Having had an opportunity for close study of Whitfield’s origi- 
nals and also the fine collection of Mr. Walcott (now in U. S. Na- 
tional Museum), from same locality, there is but little doubt that 
the specific name is correct. 
‘TARPHYCERAS (?) CONVOLVENS. 
DISCOCERAS CONVOLVENS, Angelin et Lindst. (Fragm. Si/., xvi, Fig. 
ae mot Pl, Pig. 5)s 
This form has the sutures and similar position of siphuncle and 
last part of outer whorl free and the lines of growth similar to other 
species of this genus, as figured on Pl. xvi of Angelin and Lind- 
strom. ‘The figure in section on Pl. x, Fig. 5, is doubted, because 
the whorls appear to be closer coiled and the dorso-ventral diame- 
ters increase faster than in other specimens figured. 
Lurystomites. 
This genus was first described by Schréder,* who saw that the 
Nautilus Kelloggi of Whitfield was generically distinct from his 
genus Estonioceras. He also included in the same genus /Vautilus 
Champlainensis, but this, with See/eyz and similar discoidal forms, 
are here placed in the genus Tarphyceras. 
The siphuncle is subventran in the nepionic and ananeanic sub- 
stages, becoming extracentroventran in all the later stages of devel- 
opment, or it may remain nearer the venter. The rate of growth 
of the shell is more rapid than in Tarphyceras and there are fewer 
whorls in the same diameter. ‘The ventro-dorsal diameters are 
consequently longer in proportion than in Tarphyceras. The whorl 
may be rounded until a late stage of development, but usually 
acquires a more or less flattened venter and primitive lateral zones 
and ill-defined umbilical zones like those of some species of Tar- 
phyceras. The lateral zones are apt to be more convergent and 
the abdomen narrower. 
* Op. cit., Pal. Abh. Dames et Kayser, V, p. 26. 
PROC. AMER. PHILOS. SOC, XxxII. 143.3 D. PRINTED JUNE 22, 1894. 
