84 PALAEOZOIC CORALS AND FORAMINIFERA. 



across it ; a further difference is constantly observable between 

 those groups in the vertical section, which is, that the interstitial 

 vesicular plates of the inner area in Strombodes have their rows 

 either nearly horizontal or inclining obliquely upwards from the 

 axis towards the outer wall, while in Nemaphyllum on the con- 

 trary they converge towards the axis above and incline down- 

 wards and outwards below, so as to meet at a considerable angle 

 those of the outer area which incline in the usual direction up- 

 wards and outwards towards the walls ; this peculiarity in the 

 inclination of the interstitial vesicular plates of the inner area 

 produces a marked difference in the stars on the weathered sur- 

 face in the two genera, causing the inner area to form a large 

 prominent oval or conical boss in Nemaphyllum, and a flat or 

 deeply hollowed cup in Strombodes. A third difference between 

 those generic groups is, that in the latter the vertical radiating 

 lamellae are principally confined to the inner area, not existing 

 in most of the species at all in the outer area, and do not reach 

 the walls, while on the contrary all the radiating lamellae in Ne- 

 maphyllum arise from the outer walls, are strongest in the outer 

 area, and only half of them in general penetrate the inner area. 

 In the latter corals also the whole vesicular structure is much 

 more minute and delicate in stems of the same size than in the 

 others, and the cells of the inner area are larger than those of 

 the outer, which is the reverse of what we find in Strombodes. 

 As the young columns are produced from circular buds conti- 

 nuing their development within the walls of the parent, it results 

 that the stems are inseparably united ; the walls defining the stars 

 being one simple plate, the joint production of the adjacent 

 polypes, cannot be divided, and consequently vertical fractures of 

 the mass, instead of exposing the flat, striated external surface of 

 the stems, pass invariably through the substance of the coral 

 itself, exposing only sections of the interior ; the external walls 

 being only seen in those rare cases showing the extreme limits of 

 a mass, or where in a section two masses may have coalesced. 

 Some of the species resemble Clisiophyllum, but are distinguished 

 by the peculiar axis and by the cells of the inner area being 

 larger and fewer than those of the outer. The genus is I believe 

 exclusively palaeozoic. 



Nemaphyllum arachnoideum (M^Coy). 



Sp. Char. Stars with from four to seven angles, and averaging 

 from 6 to 9 lines in diameter ; axis very thin, 1 line wide : ver- 

 tical section, inner vesicular area wider than the outer, of little- 

 arched plates inclining slightly downwards from the axis; it 

 takes about two of those plates to reach from the axis to the 

 extent of this area, or two irregularly elongate unequal cells 



