32 INTRODUCTION. 



The foregoing statements will be found to apply, more or less fully, to all the families 

 into which the Brachiopoda are subdivided by Mr. Davidson, except the DiscinidcB 

 and LivgulidcB, in whose shells a different type of structure prevails, which will be 

 described in the special account of those families. 



Family— TEREBRATUIJDJE. 



The shells of all the genera included by Mr. Davidson in this family, exhibit the 

 structure previously described, in its most characteristic form ; and all of them are 

 perforated by the system of passages which give place to the caecal prolongations of 

 the lining membrane. It is interesting to remark, that these passages do not exist in 

 the calcareous ' loop,' whose structure is in other respects precisely the same as that of 

 the shell. (PI. IV, fig. 2, a a, and fig. 10.) The following is the list of species, recent 

 and fossil, which I have examined ; the former including all those contained in the 

 unrivalled collection of Mr. Cuming, to which that gentleman has kindly allowed me free 

 access for that purpose. Of the recent species marked *, I have been enabled to make 

 transparent sections, chiefly by the liberality of Mr. Cuming in furnishing me with 

 specimens for that purpose ; the remainder have been determined by the examination of 

 the surface alone ; but the source of fallacy which has been already shown to render this 

 method insufficient as regards the fossil Brachiopoda, does not exist with respect to the 

 recent, since it is impossible for any practised observer to confound, in the latter, 

 siiperjicial depressions with actual perforations. Of all the fossil species enumerated 

 under this and other heads, I have made transparent sections ; deeming it unsafe to speak 

 in regard to them from superficial examination alone. 



Terebratula. — Recent, T. dllatata, glohosa, uva, vitrea ; — Fossil, T. Bentleyi, 

 biplicata, hullata} carnea, coarctata, fimbria, glohata, grandis, intermedia, maxillata, 

 jjcrovalis, punctata, sacculus, Salteri ? (see Retzia, p. 34), spharoidalis, squamosa. 



Waldheimia. — Recent, W. australis *,^ californiana, cranium, flavescens, Grayii, 

 lenticidaris, picta ; — Fossil, cornuta, digona, impressa, numismalis, ohlonga, obovata, 

 ornifhocephala, resupinata. 



recent Rhrjnconella psittacea, of whose structure I had given illustrations, in the Memoir with which 

 Professor King must have been acquainted (Reports of British Association for 1844), sufficiently ample, it 

 might have been thought, to make him pause before committing himself to such a sweeping assertion. To 

 myself, personally, it is a matter of entire indifference, whether Professor King does, or does not, admit the 

 correctness of my observations ; but I would submit that the interests of science are not very likely to 

 be promoted, by this easy setting-aside of observations, made with every advantage of first-rate instruments 

 and careful preparation of specimens, in favour of glances with a hand-magnifier at shells whose surfaces are 

 peculiarly liable to present deceptive appearances, the examination being confined to their exterior, and no 

 adequate means being taken to examine their intimate structure and arrangement. When Professor King 

 shall have demonstrated the existence of a system of shell-canals in Rhynconella psittacea, it may be 

 reasonably permitted him, "to doubt the absence of perforations in any Brachiopod whatever." 

 1 PI. V, fig. 1. 3 PI. IV, figs. 1—10. 



