186 DE. T. DAVIDSON OX RECENT BKACHIOPODA, 



whilst departing from the general Brachiopodons type in this respect, the shell of Crania 

 is quite conformable to it, in being penetrated by canals which are prolonged from the 

 lining membrane of the shell, and which pass towards its external surface. These differ 

 from those of Terebratula, however, in not arriving at that surface, and in breaking up 

 into minute subdivisions as they approach it. They usually open near the internal 

 margin of the valves, by orifices so large as to be apparent to the naked eye, but nearer 

 the central part of the valves, their orifices are frequently so minute as not to be readily 

 discernible. Tliis is in consequence of the formation of an additional lamina within the 

 old one, and of the contraction of the canals in their passage through it." 



Prof. King states that " Crania anomala agrees with the Ancylobrachs in having 

 both valves perpendicularly perforated ; but this character is not, as iu them, distinctly 

 manifested on the outer sui'face of the shell. In the upper valve, the perforations, 

 somewhat slender, are widest at their base, that is, where they open out on its inner 

 surface ; in other w^ords, their apertures, when observed with a high magnifying power, 

 are seen to be funnel-sliaj)ed, separated from one another by a tolerably well-defined, 

 ridge-like space ; but, with a low power, they simply appear to be separated by a space 

 approximately equalling their own diameter. The apertures occur on the whole of the 

 inner surface of this valve ; and they also occur on the corresponding surface of the 



lower one Leaving the contracted portion of their funnel-shaped base, the 



perforations pass upwards, with a slight attenuation, towards the opposite surface of the 

 valve ; but generally, on reaching the brown layer, they become divided, each one 

 sjilitting into three, four, or more widely diverging branches ; occasionally this takes 

 place before the perforations leave the white layer. The branches on approaching the 

 dark-coloured or epidermal portion of the external layer, become minutely subdivided 

 into from two to five branchlets, which appear like arborescent tufts. The branchlets, 

 belonging to the immediately adjacent perforations, become intermixed, causing the 

 intervening spaces, when viewed as a transparent object, to appear as if marked with 

 an irregular net-v/ork of very fine lines. It is difl&cult to determine whether the 

 branchlets terminate in the epidermal portion of the exterior layer. Both the branches 

 and branchlets are sub radially disposed ; an arrangement which is, however, much 

 disturbed near the margin of the valve owing to their tendency to this part. 



" As regards the intimate structure of the flat or under valve, which is habitually fixed 

 by its entire surface to stones and other foreign objects, I am only imperfectly acquainted 

 with it ; all I can say is, the apertures of the perforations are widely funnel-shaped, and 



less regularly disposed than those already noticed A vertical section, obtained 



from a specimen of C. anomala, shows that the outward growth of its upper valve is occa- 

 sionally interrupted ; which is manifested by the continuity of the external brown layer 

 being here and there broken." 



The animal of C. anomala seems to have been partially described and figured for the 

 first time in 1788 by Otto Frederic Miiller. He gave enlarged illustrations showing the 

 position and shape of the labial appendages, which extend horizontally, each forming a 

 plume-like curve, the fringe side being outermost. He likewise figured the vascular 

 impressions and some of the muscles. He styled the animal "Vermes singularissimus" 

 and while placing it in the genus Patella, admitted that on close inspection the shell 



