CotE—On Hemitrypa hibernica. 139 
- M‘Coy’s figure are on the floor of the infilled interstices of the 
tegmen, and are thus depressed; they are smooth and lustrous 
surfaces, of the same light-gray colour as the tegmen, and perhaps 
represent an adherent calcareous infilling of the aperture anterior 
in origin to the final choking of the whole structure. 
After numerous measurements, the structure being entirely the 
same, I have utilized Mr. Kirwan’s specimens from Co. Galway in 
supplying some of the detailed matter in the above description 
of Hemitrypa hibernica. In such a Fenestellid there are three 
seemingly independent points of structure that may be employed in 
comparing one specimen with another. These are (a) the number 
of columns or branches in 1 cm. ; the number of rows of fenestrules — 
will be the same as this, and the number of rows of tegminal 
apertures, measured tranversely, will be double this figure; (0) the 
number of tegminal apertures in 1 cm., measured longitudinally ; 
this, as we now know, agrees with the number of zocecial apertures, 
which is often more difficult to measure directly ; (c) the number 
of fenestrules in 1 cm. measured longitudinally. To ascertain 
precisely the value of these quantities in specific determination, I 
tabulated six Irish specimens in the following three ways, adding 
Prout’s Fenestella hemitrypa and Ulrich’s H. proutana for compari- 
son, since the general structure in all these seemed very closely 
similar. 
The specimens thus used are :— 
1. Probable type of H. hibernica, Griffith collection, from 
Lower Carboniferous Limestone, Little Id., Cork. A 
larger specimen from the same locality agrees so pre- 
cisely as not to require separate tabulation. 
2. Specimen labelled Hemitrypa hibernica, from Upper Carboni- 
ferous Limestone, Knockninny, Enniskillen. Griffith 
collection. 
3. Specimen similarly labelled, from Calp, Ballintrillick, Bun- 
doran. Griffith collection. 
4. Specimen collected by Mr. Kirwan, from Carboniferous 
Limestone, Gardenfield, Co. Galway. 
4a. Ditto, in darker limestone. 
4b. Ditto, small specimen, in darker limestone. 
5. From Prout’s description of his Carboniferous F. henutrypa. 
6. From Ulrich’s description of typical H. proutana. 
