﻿14 T. Davidson — On New Scottish Brachiopoda. 



quoted.^ These tubular spines measure about one line in length and 

 are seemingly straight and smooth, and do not, any more than those 

 figured by Kutorga, show that peculiar moniliform character so well 

 described and figured by Morris in the much longer spines of liis 

 Sipli. Anglica. Mrs. Gray's largest specimen would not exceed 

 seven lines in length by six in breadth, and has much the general 

 shape of young specimens of SipJi. unguiculata. 



Before dismissing the subject of the structure of Siphonotreta, I 



1 Prof. "W. King has kindly favoured me with the following remarks he had made 

 on the shell and spines of one of the Eussiau 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 considerable 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 ' perforated structure ' ; also that their outer surface is 

 ornamented with numerous tubular spines, generally arranged in a very regular 

 order, leaving, when broken oif, 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 ' 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 trimcated, exhibit very clearly the 

 position of their contained tube ; besides, the 

 pimples frequently show a hollow, correspond- 

 ing to the tube, in their centre. The inner 

 surface of the valve is marked with regular 

 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 



®^p ^p is not satisfactorily exhibited, evidently through 



^ ^^ molecular changes which the intermediate layer 



^^ /^ (® ^^ ^^^ valves has undergone. From the pre- 



^^ ^ w ceding remarks it will be seen that the spinose 



Fie- B X 105 peculiarities of Siphonotreta unguiculata, in- 



°" ■ ' stead of being simply dermal ^'I'ocesses, as is 



the case in Discina, are of the nature of those known to characterize Productus, 

 iStrophalosia, Bh. 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 Terehratula, Spiriferina, and other genera of their class, 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 iufiUing ; 

 and frequently they are charged with a greenish subtranslucent mineral substance, 

 which certain Canadian Eozoouites, 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 qiiestion 

 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 fact may be offered as further supporting the conclusion that there is a tubular 

 connexion between the inner and the outer surface of the valves." 



