64 
JANE I. EOEERTSON. 
Ill tlie proximal portion of tlie bulb us there is, attached to 
the ventral wall, a solid ridge which extends to the transverse 
part (PI. 5, figs. 1 and 3, S^)- V. p.) ; this ridge or valve is 
inserted along the middle line of the ventral bulbus wall, com- 
mencing at its posterior end a little anterior to, but imme- 
diately in line with, the interventricular septum (PL 5, figs. 
1 and 2, V. S., and /S'p. V.j).) ; proximally it tapers off rapidly 
into the bulbus wall, but distally it broadens considerably, 
while its somewhat flattened end projects forwards into the 
lumen of the transverse part of the bulbus (PI. 5, figs. 3 and 
4, S j). F. jj.) . On this valve near its origin there is always one 
distinct transverse ridge, in front of which again one or two 
more or less faint transverse furrows are usually to be distin- 
guished (PI. 5, figs. 1 and 3, t. f.) ; these recall the superim- 
posed valves from which the spiral ridge is believed to have 
been evolved in phylogeny. At the same level, traces of 
vestigial pocket valves ( 17 ) are present on the lateral and dorsal 
walls of the bulbus cordis ; these are represented usually by 
thi-ee rows of tiny ridges arranged three in each row with still 
tinier irregular vestiges between (PI. 5, figs. 1 and 3, u, h, c). 
In one case, out of eight hearts examined, only two vestigial 
valves could be distinguished in each row. The proximal 
ridges, those nearest the ventricle, are always most prominent. 
As the transverse part of the bulbus is reached, the 
valvular ridge on the ventral wall of the first part is con- 
tinuous with the ledge projecting from the dorsal wall of the 
transverse part (PI. 5, figs. 1 and 4, S]?. V. t.). This vertical 
ridge in the transverse part is usually distinctly concave on 
its posterior surface, but in one instance it was characterised 
by the dorso-ventral flattening of its free ventral margin so 
as to give it in consequence a somewhat J_"shape. In the 
distal part of the bulbus the valve becomes more flattened, 
has a free left border, and is attached along the right wall 
(PL 5, figs. 2 and 4, Sp. V, d.) ; these continuous valve-like 
structures curving along the length of the bulbus cordis 
constitute the spiral valve. In the distal part of the bulbus 
there is also a second longitudinal valve-like projection 
