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SUPPLEMENT TO THE BRITISH 
number of their convolutions, so that in some specimens one coil will occupy a larger 
portion of the interior of the shell than the other. The number of spiral convolutions is 
also found to be variable Avhen comparing different specimens of the same species; they 
are nsnally fewer in number and comparatively further apart in the young shell, and 
seem to increase in number with the growth of the animal. The laminae forming the 
coils seem to be also closer in some specimens than in others. 
The direction of the spirals in the Spiriferidae varies to some extent, even in different 
specimens of a same species, namely, their extremities are always a little higher or 
lower towards the posterior lateral margins of the shell, but in a more or less standing 
direction towards the cardinal extremities ; this will be seen in the different figures of 8j). 
lineaia, shown in PI. XXXII of the Supplement. 
The principal stems of the spiral coils, after having been attached to the hinge-plate, 
converge to about one third of the length of the shell, when, giving off a short lamella, or 
crural process, they diverge again rapidly and widely as they near the front ; when by a 
sudden inward curve the two principal stems come again nearer to each other, until they 
reach the posterior portion of the valve, and thus form the first coil (see Sup., PI. XXXI, 
figs. 3 and 3 a ; and PL XXXII, figs. 6 and 6 a). 
When, as is apparently the case in Sjnrifer lineata, var. imbricata, the principal 
stems converge to more than half the length of the valve before diverging, the spiral 
cones direct themselves in a V-shaped manner to the cardinal extremities of the shell, as 
is seen in Sup., Pi. XXXII, figs. 6, 6 a 3, 7. These variations in the position and direction 
of the spiral coils are well exemplified in the admirable series of specimens developed by 
the Rev. Norman Glass. Figures of these will be found in Pis. XXXI, XXXII, and 
XXXIV of this Supplement. It is impossible to say too much of the remarkable skill 
with which he has worked out so many specimens, and I feel very grateful to him for 
the valuable and valued help he has so kindly afforded me. 
Finely developed specimens of Spiriferitice from the Liassic formations of Normandy 
were worked out many years ago by M. Eudes Deslongchamps, but he had to deal with a 
different and softer matrix than that in which Mr. Glass has achieved his results. Some 
finely worked-out specimens of American Palaeozoic Spirifers and other genera have been 
described and illustrated by Prof. Hall and Mr. Whitfield, and to these we shall have 
occasion to allude in the sequel, but in this case the results were obtained principally in 
siUceous specimens or by sections, and not developed in spar by the process Mr. Glass 
has discovered. Prof. Hall and Mr. Whitfield have wonderfully succeeded in developing 
the complicated connecting processes or lamellae that exist between the two principal 
stems of the spiral processes in Atrypa^ Athyris, Merista, Meristella, and other spiral- 
bearing genera. Mr. Glass's process does not seem to be favorable for achieving a 
like result, but, as will be shown in the sequel, Mr. Glass has been able to work out the 
connecting processes or loop formed by the first coils of the spirals in Meristella tuniida 
and Atrypa reticularis. 
