220 Mr. R. Etheridge and Dr. H. A. Nicholson 
with Prof. de Koninck; but we think that one of these names, 
P. cymba, may with all propriety be retained as a good varie- 
tal designation for the young conditions of the species, one 
state of which, we believe, Von Seebach’s figure to repre- 
sent*, whilst we shall describe a still more juvenile form imme- 
diately. Amongst the specimens forwarded to us by Mr. 
Perceval are three examples, two of which have evidently 
undergone a good deal of lateral compression; otherwise the 
form, of one of them at least, we believe, would have approxi- 
mated to the figure of P. cymba, Von Seebach—transversely 
elongated in relation to the breadth, sharp below, and bearing 
well-marked terminal cells or cups, as in the figure above 
quoted. This specimen bears traces of four cups; but the 
other two individuals, it is quite clear, only had two, and, 
according to our view, represent the youngest state of the 
species. One of these little specimens (PI. XII. fig. 15) has 
the cuneate form below, the slightly sinuous basal edge, the 
flattened sides expanding upwards, and the transversely elon- 
gated calices seen in some of the figured examples of P. obtusa, 
var. cymba. hat it would be very unlikely to develop into 
such a form as P. cunetformis is apparent when compared 
with the figures we give of. the young state of that species 
(Pl. XII. figs, 11, 12); whilst quite the same remark 
applies to the young condition of P. cyclostoma, with its in- 
variably expanded base of attachment. Assuming, therefore, 
that our figure and Von Seebach’s figs. 4, 4a], represent 
various stages in the growth of P. obtusa, it is for such forms 
that we would retain the varietal name P. cymba, whilst 
Meek and Worthen’s figures t, and Von Seebach’s figures of 
his P. umbonata §, will represent the mature colony, so far as 
it is at present known to us. 
Paleacis obtusa may at once be distinguished from the other 
species of the genus :—from P. cunecformis, H. & Edw., by 
its wide cuneate form, obtuse. basal carina, with the sides at 
first flattened, then gradually expanding upwards, and the 
extended upper surface; from P. cyclostoma, Phill. (which 
it much more closely resembles in the number of its cups in 
the adult state, and the extended upper surface of the colony), 
by the presence of the obtuse basal carina, more cuneate 
form, and total absence of the broad base of attachment of 
Phillips’s species. 
In the structure of its surface-ornamentation P, obtusa 
approximates to P. cuneiformis. 
* Zeitschrift, loc. cit. f. 4, 4a. + Loe. cit. 
{ Illinois Geol. Rep. ii. pl. 17. f. 2, a-e. 
§ Zeitschrift, loc. cit. f. 3, a-c. 
