Mr. W. Lonsdale on the Genus Lithostrotion. 471 



of which, or every alternate plate, ranged to the centre, not in a 

 straight line, hut more or less waved; and the intermediate 

 lamella? stopt at what was supposed to have been the boundary 

 of the central swelling. The dissepiments were likewise very 

 numerous in the outer portion of the corallite, though not redu- 

 cible to circles, being extremely irregular in position, distance 

 and outline ; while in the supposed axeal area they were much 

 fewer. The breadth of the outer zone was about half that of the 

 semidiameter of the corallite. In Cyathophyllum basaltiforme 

 two portions probably exist, as * the marginal lamellae " are said 

 to li commence within a thin, crenulated, vertical dissepiment," 

 and judging by the illustrative figures 21 and 22, the width of 

 the areas is similar to that in the Kendal fossil. The outer part 

 of Columnaria is i( cellular," and its breadth bears to the inner 

 the proportions just mentioned ; equivalent characters as well as 

 measurements occur also in NemaphyUum. Lastly, in Stylastrea 

 the outer zone is largely cellular, the lamelke and dissepiments 

 being distant, but the dimensions agree with those in the other 

 basaltiform fossils. 



A comparison of the characters just enumerated in the exte- 

 rior area of branched and massive species of Lithostrotion (Ar- 

 chives), so far as they are known in the latter, and in apparently 

 allied fossils, will give the following differences : — in Mr. Phil- 

 lips's fossils the structures are reducible generally to one type — 

 a series of small cells adjacent to the walls, and another within 

 of larger dimensions, the two being separated more or less pro- 

 minently by a circle of arched plates ; and the breadth of the area 

 is small, sometimes almost inconspicuous : on the contrary, in 

 the massive corals the cells cannot be brought to a definite ar- 

 rangement or shape, except in Parkinson's fossil, according to 

 its description, and in that case there is no distinction between 

 the cells next the wall and those situated elsewhere ; the breadth 

 of the area is also relatively great in every case, equalling almost 

 uniformly half the semidiameter of the corallites. 



Little can be said respecting the lamellae, and that little is 

 given chiefly to excite inquiry. In the ' Archives f they are stated 

 to be pretty well developed — u cloisons assez bien developpees ;" 

 and in the ' Geology of Yorkshire ' to be " generally twisted or 

 extinct near the centre." The latter characters were fully exhi- 

 bited in the specimens examined during the present inquiry ; but 

 nothing is believed to have been published respecting the want 

 of vertical persistence in the inner area ; though such a condi- 

 tion is intimated in the remark, that the lamellae are sometimes 

 twisted near the centre, and sometimes extinct, as if the exten- 

 sion had depended on variations in growth. No evidence wholly 

 satisfactory respecting this point has been obtained; nevertheless 



