68 BRITISH PALAZOZOIC FOSSILS. [Zoopuyra. 
averaging two inter-diaphragmal spaces to the width of the tube; usually about four polygonal tubules in 
the shortest line between adjacent tubes; diaphragms in the polygonal tubules, about half their diameter 
apart at the concentric bands of renewed growth, rather more than their diameter apart between these bands. 
This species, so often confounded with the Silurian P. interstincta, is clearly confined to the Devonian 
system, both in this country and on the continent, and is easily distinguished therefrom by the much greater 
distance of the lamelliferous tubes and much larger number of the interstitial tubules, which latter more 
usually exceed the above average than fall below it. Care must be taken to examine specimens rubbed flat, 
as many specimens shewing a weathered surface have a deep depressed circular space round the mouth of 
each tube, increasing its apparent diameter, and giving a deceptive appearance of narrowness to the interven- 
ing spaces. I have seen one rare specimen in which the cell-tubes are only half a line in diameter, but the 
average distance from centre to centre was the same as in the other specimens; it agrees with Phillips’s 
figure, and is named Phillipsii by d’Orbigny in his Prodrome. 
Position and Locality—vVery abundant in the Devonian limestone of Newton Bushel and Teignmouth. 
Genus. FAVOSITES (Lam.) See page 19. 
FAVOSITES POLYMORPHA (Go/d.) 
Ref—Gold. Pet. Germ. t. 27. f. 2, 3, 4. 
Sp. Ch—Corallum forming thick, curved, cylindrical branches, averaging five to fifteen lines in diameter, 
composed of polygonal tubes, averaging two-thirds of a line in diameter, but with numerous smaller, irre- 
-gularly interpolated ones ; the tubes are nearly vertical in the middle of the branches, arching outwards 
to the surface, on which they open obliquely; the walls are thin, polygonal, and prismatic in the interior, 
and in old specimens greatly thickened to render the aperture small and round towards the surface ; 
averaging three cell-openings in the space of two lines; internal diaphragms very thin, irregular, oblique or 
horizontal in position, averaging two inter-diaphragmal spaces to the diameter of one tube; connecting 
pores large, one row on each face, nearly the diameter of the tubes apart. 
This extremely fine, well-marked species, is remarkable for the size of its branches, and the great thick- 
ness which the walls assume towards their oblique termination on the surface, rendering the interior of 
the tubes cylindrical, as well as the comparative shortness and great number of the interpolated young 
tubes, arising from their rapid divergence. I doubt its occurrence in Silurian rocks (see /’. crassa, p. 20). 
Position and Locality—Extremely abundant in the Devonian limestone of Newton Bushel, and Teign- 
mouth ; and in the shales of Newquay and S. of Plymouth, and slates at Bedruthen Steps in St Eval. 
Genus. ALVEOLITES (Lam.) as redefined. 
Gen. Char.—Corallum polymorphous, composed of irregular, superposed concentric layers of short pris- 
matic tubes, with very thick common inseparably united walls, traversed by numerous horizontal diaphragms, 
and pierced by distinct communicating pores; cell-openings very oblique to the surface, semicircular or 
rhomboidal, lower margins most prominent; tubes increasing occasionally by dichotomous fissure. 
I have noticed the dichotomous fission of the transversely septate tubes, both in the true F’. spongites 
of the Eifel (which, with MM. Milne Edwards and Haime, I take as the type of the genus Alveolites) and 
in our British A. vermicularis, shewing that in this respect and the consequent community of the walls, 
this genus is more nearly related to Chetetes than to Favosites, while by its communicating pores it is 
most allied to the latter, and differs from the former. 
