300 DESCRIPTION OF CHALK CORALS. 
to state, that no agreement whatever exists between Mr. Dixon’s zoophyte, and 
the species of Adeona represented by Lamouroux and other authorities!. The 
foregoing remarks show that in some characters the subject of this inquiry ac- 
cords with more than one established genus, but that it differs in the aggregate 
of structures in each case ; and the compiler of these memoranda, believing that 
the peculiar layer which forms the exterior does not exist in any described Bryo- 
zoa, as well as that it was developed by a most important part of the polype, 
proposes to distinguish the fossil by the term Siphoniotyphlus (oupomoy tubulus, 
tupAdc cecus), in allusion to the closed or blind tubuli constituting the lamina. 
Siphoniotyphlus, n. g. 
Tubular, tubes invisible externally as respects range and outline at all periods 
of growth, slightly or not at all superimposed ; additional tubes formed at or 
near the extremity of pre-existing ; exterior a thin layer closely united to the 
visceral cavities, and composed of microscopic tubuli without surface-apertures ; 
developed also contemporaneously with the primary tubes. 
Siphoniotyphlus plumatus. (Tab. XVIII. B. figs. 2 & 2a.) 
Slender, elongated, slightly convex expansions, formed of two opposite layers 
of tubes ; apertures slightly protruded, disposed in transverse rows diverging 
from the centre and occupying about half the breadth of the expansions ; surface 
lamina extended laterally in a thin band without tubular apertures ; interior of 
middle area wholly occupied by abdominal tubes ; external changes due to age 
slight. 
The specimen on which the present notice depends, forms part of the series 
obligingly lent by Mr. Dixon for examination. The greater part is represented 
of the natural size in figure 2; and the blow which had detached the upper por- 
tion (fig. 2*) had happily exposed a cast of the opposite surface, and proved that 
the fossil consisted of two similar layers united dorsally. The full length of the 
specimen was about an inch and a quarter, and the greatest ascertained breadth 
two lines, the tubular apertures occupying about half the transverse area; but 
this measurement must not be regarded as accurate, the margin being fractured 
nearly throughout its extent: the thickness in the middle of the expansion was 
' Exposition Méthodique, p. 39-40, tab. 70. fig. 5, or Histoire des Coralligénes flexibles, p. 481, 
pl. 19. fig. 2; consult also Schweigger, Beobachtungen, &c., taf. 2. figs. 5, 6, 7; as well as taf. 1 with 
descriptions of the plates, and p. 69; likewise De Blainville’s Man. d’Actinologie, p.431. pl. 76. fig. 2. 
