CRANIA. 9 



Diagnosis. Shell irregular, inequivalve, transversely oval, entirely attached by the 

 substance of the lower valve to rocks, corals, echinodermata, &c, modelling itself to the 

 object of attachment, the irregularities of which it fills up to a greater or less extent ; 

 margin much elevated, especially in front, rising obliquely or even vertically all round, 

 except on the posterior side; the central portion is irregularly hollowed out; structure 

 largely cellular, spongeous or granular, particularly so round the margin; muscular 

 impressions four in number, strongly produced in different examples ; the two posterior 

 ones variably circular, larger and more widely separated than the anterior ones ; these 

 last are usually in contact, being more elongated and depressed in the centre, between, 

 and above which is seen a produced nose-shaped projection, somewhat variable in its 

 details in different individuals ; the digitated vascular impressions are likewise more or less 

 marked. Upper or unattached valve thin, conical, patelliform, very convex, exteriorly 

 covered by small granular asperities ; vertex sub-central, with numerous concentric lines of 

 growth. In the interior four deep muscular impressions; two irregularly circular or oval 

 ones are situated near the posterior edge, widely separated, and corresponding to those 

 seen in the same position on the attached valve ; towards the centre, other two elongated 

 muscular impressions are visibly in contact at their base, and forming long narrow uneven 

 projections, detached, except at their origin, from the bottom of the shell, and directing 

 themselves towards the lateral portion of the valve. Structure punctuated ; dimensions 

 variable. Length 7, width 11, height 4 lines. 



05s. This remarkable species has been fortunate, all authors having applied to it the same 

 denomination, — an occurrence very rare among the Brachiopoda. It is frequently found 

 in the Upper Chalk of many localities, but is a very irregular shell, few specimens bearing 

 exactly the same shape ; it is always attached by the whole surface of its lower valve, and, 

 as stated above, modelling itself and filling up all the projections or depressions existing 

 either on the rock or shell to which it is united, so that it cannot be detached from the 

 place where it is fixed, provided this last is of a solid nature ; but I have specimens that 

 were joined during life to soft and perishable bodies, such as sponge, &c. One remarkable 

 specimen, belonging to Mr. Catt of Brighton, presents an exact cast of the structure of a 

 ventriculite to which it was fixed ; it therefore remains very uneven and contorted where 

 the object was rough and angular. In the Upper Chalk of Meudon this species is often 

 met with, and I have picked up there specimens of Ananchytes, covered by more than 

 fifteen or twenty individuals of all ages, illustrating in the clearest manner their formation. 

 In the very young state the shell of the lower valve is so thin, except at its margin, that 

 every accident of the object it sticks to is apparent and reproduced, the muscular impres- 

 sions are faint and scarcely defined, the margin alone assuming a thickness ten or twelve 

 times more considerable than that of the other portion of the valve ; by degrees, however, 

 as the shell acquires age, by successive layers of calcareous matter, it presents a greater 

 and an unequal thickness, filling up and concealing the largest portion of the asperities 

 existing on the object of attachment. Much difference may be noticed, likewise, in the 



