DK. T. DAVIDSON ON RECENT BRACHIOPODA. 19 



Hab. Spitzbci'gen and Davis Straits ; uortli-east European seas ; Oban and off Cumbrae 

 Islands, Loch Torridon, Scotland; off Belfast; Finisterre and Croix de Gavic; Morl)i- 

 han ; Cape Breton ; Adventure Bank ; off Guetaria, Spain ; north-east coast of Jamaica ; 

 Corea and Sagami Bay, Japan, &c. 



Fossil. In the Upper Tertiaries of Sicily ; Coralline Crag of England, Belgium, sontli 

 of Spain, Azores, &c., &c. 



Obs. No species of Bracbiopoda has been more thoroughly or more carefully studied 

 than the Anomki caput-serpentis of Linne. It is a very common and well-knoun 

 species, abounding in the localities where it is found, and has since 1767 attracted the 

 attention of a large number of malacologists. 



The shell varies somewhat in shape and especially, according to age, in the number 

 of its ribs. These modifications have been often described by myself and others, and 

 most recently, in 1881, by M. E. Deslongchamps *. In tlie youngest condition the 

 shell tapers posteriorly, and is widest anteriorly ; the hinge-line is then almost strain-bt. 

 the auricular expansions comparatively larger, the foramen triangular or elongated oval. 

 In a specimen, less than a line in length, forwarded for my examination by the Marquis 

 de Eolin, the posterior half of the valves was smooth, while on the anterior half some 

 seven, scarcely developed, rounded radiating ribs were present. At one and a half line 

 the surface of each valve was ornamented with about ten simple rounded ribs Avith 

 interspaces of about equal breadth, concentrically crossed by equidistant projectiui;- 

 ridges, most prominent on the surface of the ribs. As the shell grows lar"-er, tlie 

 auricular expansions become smaller, the hinge-line obliquely or obtusely angular, the 

 ribs more numerous and finer, the lines of growth less prominent, and the greatest 

 breadth at about half the shell's length. Similar important modifications take place also 

 in the interior of the valves. In the interior of the dorsal valve, when quite vouui;', 

 and up to a certain age, the crura are widely separated ; but as the shell grows, the 

 pointed extremities facing each other extend nearer and nearer towards each other until 

 they become united and form a well-defined band, giving the loop an annelliform sha])e 

 and character. 



The intimate shell-structiu'e of T. caput-serpentis has been described and fi'i-ured l)v 

 Dr. W. B. Carpenter, Oscar Schmidt, Prof. W. King, E. Deslongchamps, and others. 

 Dr. Carpenter says that it is in T. cajyut-serpentis "that tlie canals are of smallest 

 dimensions, their largest diameter being about jinjo of an inch, whilst their averao-e 

 distance from each other is about the same as in the preceding case \_JFaldheimia 

 Jlatescens, -j^ inch] — their regular arrangement, however, being so modified, that the 



external orifices are principally seen upon the elevated parts of the plications, 



whilst they open internally in similar rows." 



When alluding to the shell-structure of T. caput-serpentis, in his valuable memoir on 

 the histology of the test of the Palliobranchiata (Trans. Roy. Irish Acad. vol. xxiv. 

 p. 148, 1869), Prof. W. King says : — " The species just mentioned, which is longitudinally 

 ribbed, has two kinds of perforations : those lying in the furrows are simple ; while those 



* ' Etudes, critiques sur des Brachiopodcs nouveaux ou peu connus :' Caen, 1884. 



3* 



