619 
PrAT EH) ll. 
Figs. 1-6. Mimoceras (Gontatites) compressum, after Branco, Paleontogra- 
phica, xxvii, Pl. viii, much enlarged, to show the loose mode of coiling, absence 
of impressed zone, primitive nautiloid sutures of the young until a late stage, and 
protoconch joining the conch without any constriction on the sides or abdomen, 
but with a slight constriction on the dorsum, showing tendency to coil, these 
being typical ammonitoid characteristics. Fig. 6, 1 and 2and x represent the 
first, second, and older septum, the septa of the later stages are shown with ven- 
tral siphonal lobe in Fig. 5. Fig. 20 is the same species after Sandberger. 
Figs. 7 and 8. Mzmoceras (Goniatites) ambigena, after Barrande, Systeme 
Silurien, Pl. iii, Fig. 22,and PI. xii, Fig. 7, showing the absence of an impressed 
zone at a late stage, probably the ephebic stage of development. 
Figs. 9-11. Agontatites (Goniatites) fecundus, after Barrande (7207¢.), Pl. x, 
Figs. 13-15, showing the absence of the impressed zone until a late stage; Fig. 
II is nearly natural size, and this shows, when compared with others of Bar- 
rande’s figures of this species, which have the impressed zone in adults (Bar- 
rande, Pl. vii, Figs. 10 and 11), that this characteristic comes at a much earlier 
stage in some specimens, and is originated by close coiling, as it is in Agoniatites 
Vanuxemi, but at an earlier stage than in 4. fecundus. 
Figs. 12 and 13. Agoniatites (?) (Goniatites) crebriseptus, after Barrande 
(zézd.), Pl. vii, Figs. 1 and 2, reduced one-third, showing how similar to some 
nautiloids the adults of this genus may be, both in form and sutures,* with the 
exception of the ventral siphonal lobe, which alone enables one to place them 
among Ammonoids. 
Figs. 14 and 15. Agoniatites fecundus, after Barrande (zd7d.), Pl. xi, Figs. 2 
and 4, enlarged to show the variation of the coiling of two varieties in the pro- 
toconchial and nepionic stages. These are both included under one name by 
Barrande. 
Fig. 16. Anarcestes (Gontatites) lateseptatus, after Branco, of. ci¢., xxvii, 
Pl. vi, enlarged, showing the immature ventral sutures of this with the primitive 
undivided siphonal lobe beginning in the second septum of the metanepionic 
substage. ‘This continues substantially the same in aspect throughout life in the 
genera Mimoceras, Anarcestes, Agoniatites and Pinnacites, all Silurian forms of 
Goniatitinee. 
Figs. 17-19. Gephuroceras (Goniatites) serratum, after Branco, of. cit., xxvii, 
Pl. vi, enlarged, showing sutures of Devonian Goniatitinee with accelerated devel- 
opment. The mimoceran undivided siphonal lobe is here shown in the metane- 
pionic substage, 2-4 septa, but in the paranepionic, where the coil is 3 mm. in 
diameter, the siphonal saddle arises in the centre of this lobe as a new character 
acquired in the later stages of growth. 
Figs. 20-25. These give the protoconch and young of various species of 
Goniatitinz of the Devonian after Sandberger, Fahréuch d. Nass. Verein, 1851, 
* Mimoceras ( Goniatites) lituus is a still larger form, also figured by Barrande, which has 
no impressed zone and is very similar to many nautiloids which have similar compressed 
elliptical whorl and subventran siphuncles. His figure is reproduced here in reduced 
outline, Figs. 40, 41, Pl. viii. 
