271 
The sntural markings in the Ammonites are very com- 
plicated, being what is termed foliaceous. In Goniatites they 
are zigzag, whilst in Ceratites they are alternately lobed and 
crenated. The position of the siphuncle, too, is variable in 
the Nautilidse, being central or sub-central, whilst in the 
Aramonitidae it is dorsal and external. 
The internal shells belonging to the Dibranchiate group 
may consist of : — 
a — A pen (gladius) which is horny or chitinous, as in 
LoKgo. 
/? — A Sepiostaire'^ or cuttle-bone, which is calcareous, as 
in Sepia. 
A — A more complex structure, with a chambered portion 
(phragmacone), as in Spirula. 
In Spirula the shell is entirely pearly or nacreous ; it is 
chambered, the whorls are separate, and there is a ventral 
siphuncle. Though the animal of Spirula is exceedingly 
rare, the shell is cast up by thousands on the shores of New 
Zealand. The shell contains the ink-bag.* 
Generative Organs.-^ — The Cephalopoda are dioecious. In 
both sexes the generative organs open into the mantle cavity 
by an oviduct ; they contain ova or spermatozoa according to 
the sex of the individual. Peculiar lamellated glands are 
developed in the female, which secrete a sticky substance 
which serves to coat the eggs and hold them together in 
aggregated masses ; in the male a gland provides the sub- 
stance out of which are composed the spermatophores, the 
* Tlirougli tlic kiiwlness of J. Tyornian, Esq., Tregoncy, Cornwall; tho nnim&l 
of Spirula, preserved iu spirits of ^Yinc, was cxhiliited at tho meeting of tho West 
Eiding Geological and I'olytechuic Society, held at Iluddersfield iu the autumn of 
this year (1877). It was tho same 8i)Ccimon that Dr. Jeflfreys spoke of in his 
address to the Biological Section of the British Association, held at Plymouth. 
f Sec '* Ilci-tocotyldannclaon hos Octoj)ods Itcglernc, Argonauta og Ti-cmocto- 
pus," J. J. Sm. Stoenstrup, Kjiibouh, I80G. 
