294 Dr. H. A. Nicholson’s Contributions 
similar spines exist, they are comparatively small and short, 
the surface wanting, therefore, the rough appearance which 
exists in M/. ? tumida. 
‘(d) The tabule in the peripheral region of the corallum are 
few in number in JZ. ? tumdda, and are almost invariably com- 
plete and imperforate. On the other hand, the tabulee of the 
same region in S. Howsii are numerous, and are, mostly or 
wholly, perforated by central apertures. Hence many of the 
calices in this latter type have their floors formed by one of 
these perforated tabulee. 
(e) The walls of the corallites in the peripheral region of 
the corallum are in M/.? tumida greatly thickened, but the 
thickening is approximately uniform and shows no regular 
intermissions. In S. Hows?7, on the other hand, the walls of 
the corallites in the same region are intermittently thickened, 
and thus assume a moniliform or beaded structure. 
(f) 10? tumida does not appear to possess the singular 
thick-walled circular tubes which are so commonly developed 
in S. Howsii at the angles of junction of the normal cor- 
allites. 
As to the synonymy and nomenclature of MM. ? tumida, a 
good deal of confusion has been caused by the fact (which I 
have only recently come to appreciate fully) that M7. ? tumida 
and §. Howsii have hitherto been imperfectly or not at all 
separated from one another—this being not unnatural when it 
is remembered that the two commonly occur together and are 
externally very similar. Hence some observers have either 
included both types under the name of JV. twmida, or have 
founded their descriptions of JZ. tumida upon specimens which 
really belong to S. Howsit. 
It is quite clear that Phillips himself included at least two 
different forms under the name of Calamopora tumida. One 
form (‘ Geol. of Yorkshire,’ pl. 1. figs. 49-51) is almost cer- 
tainly the form which I have, here and elsewhere, regarded 
as Monticulipora tumida. Another form (cid. pl. 1. figs. 52, 
56, 57) may be taken, with an equal approach to certainty, 
to be the type which I have here called Stenopora Howsi. 
Under these circumstances, considering the very brief nature 
of the description given by Phillips, it would perhaps have 
been best to have suppressed the name of “ tuwmida” alto- 
gether; but the wide currency which it has acquired renders 
this impossible. I shall therefore retain it for the species 
here so named; and in giving a synonymy of the species I 
should omit all the figures given by Phillips in plate 1. of his 
‘ Geology of Yorkshire,’ except figs. 49, 50, and 51. 
