14 
T. Davidson — On.New Scottish Brachiopoda. 
quoted. 1 These tubulär spines measure about one line in length and 
are seemingly straight and smooth, and do not, any more than those 
figured by Kutorga, sliow that peculiar moniliform character so well 
described and figured by Morris in tlie much longer spines of his 
Siph. Anglica. Mrs. Gi'ay’s largest specimen would not exceed 
seven lines in length by six in breadth, and has much the general 
shape of young specimens of Siph. unguiculata. 
Before dismissing the subject of the structure of Siphonotreta, I 
1 Prof. W. King has kindly fayoured me with the following remarks he had made 
on the shell and spines of one of the Russian species : — “ The valve of Siphonotreta, 
as stated by Kutorga, consists of a dermis of a horny nature, an inner perlaceous 
layer, and an intermediate one of considerahle thickness, and containing calcareous 
matter. Probably an analysis would determine the presence of phosphate of lime in 
the valves, as in those of Lingula and Discina. The dermal layer, the only one that 
could be tried, slightly effervesces on the application of acid: the same test, however, 
discloses abundance of lime in the casts of the fossils. Morris has noticed that the 
valves have a distinctly 4 perforated structure ’ ; also that their outer surface is 
ornamented with numerous tubulär spines, generally arranged in a very regulär 
Order, leaving, when broken off, slightly projecting hollow tubercules in their 
place. He does not mention that the spines are continuous with the perforations ; 
but it may be inferred that this peculiarity was not unsuspected by him. The spines 
in the specimens of Siphonotreta unguiculata under Observation are only preserved 
on portions of the valves near their margin ; elsewhere their presence is indicated 
by minute tubercules or pimples. It was these that led De Verneuil to characterize 
the shell 4 a surface chagrinee.’ Between the pimples the surface is marked with 
fine raised reticulating lines. The tubularity of the spines is indicated by an opaque 
_ medial line in the midst of their subtrans- 
Fig. A. x 105. lucent substance (Fig. A.). The spines, when 
transversely truncated, exhibit very clearly the 
\ \ position of their contained tube ; besides, the 
\ V\ 1\ CD\ 1 \1 \ \ pimples frequently show a hollow, correspond- 
\\ \ ] \ Y 1 I \ \ \ ing to the tube, in their centre. The inner 
J \ \ \J \J VJ \ surface of the valve is marked with regulär 
cup-shaped depressions (eminences on a cast of 
it), containing in their centre a minute deep 
cavity (Fig. B.) ; which is doubtless continued 
through the thickness of the valve into the 
^ tube of the external spines, but the connexion 
® is not satisfactorily exhibited, evidently through 
0 molecular changes which the intermediate layer 
Q of the valves has undergone. From the pre- 
vnr ceding remarks it will be seen that the spinöse 
Fio- jj x jpg peculiarities of Siphonotreta unguiculata, in- 
’ stead of being simply dermal processes, as is 
the case in Discina, are of the nature of those known to characterize Productus. 
Strophalosia, Eh. spinosa, and some other Palliobranchs. Whether the tubularity of 
the spines in Siphonotreta and the fossils just named, is homologous to the perforated 
shell structure common to Terebratula, Spiriferina, and other genera of their dass, is a 
question which does not seem to be sufficiently advanced for determination at present. 
Often the hollows on the inner surface of the valve contain a dark-coloured iufilling ; 
and frequently they are charged with a greenish subtranslucent mineral substance, 
which certain Canadian Eozoonites, unnecessarily anxious to meet with a case of 
the kind, would probably regard as Serpentine ; but without denying the possibility 
of such a methylised product occurring as a fossil infilling, the substance in question 
seems more likely to be one of the numerous varieties of glauconite; or possibly, it 
may be related to apatite, and derived from the phosphate of lime of which the 
shell structure of Siphonotreta was to some extent originally composed. The hollows 
in the pimples, on the outer surface, are also often filled with the same substance ; 
which faet may be offered as further supporting the conclusion that there is a tubulär 
connexion between the inner and the outer surface of the valves.” 
