RHYNCHONELLID. 203 
of the beak, extends to the front. Surface of both valves smooth, but marked by a few 
faint concentric lines of growth. 
Length 3, width 3, depth 2 lines. 
Obs. This interesting little species had some years ago received from Messrs. Forbes 
and Salter the MS. name of Rhynchonella apiculata, and this has been transcribed in the 
printed catalogue of the fossils in the Museum of Practical Geology. It is not, however, a 
Rhynchonella, and My. Salter would now refer it to Atrypa; but I am sadly at a loss to 
know where it should be placed, while Prof. Hall would suggest the proposing of a new 
genus for its reception. Unfortunately, all my endeavours to discover its internal arrange- 
ments have proved unavailing, and consequently I have provisionally left it with Atrypa, 
to which, in all probability, it does not belong. 
Position and Locality. This small shell occurs in the Caradoc or Bala Limestone, at 
the Chair of Kildare, County Kildare, Ireland; and some good examples may be seen in 
the Museum of Practical Geology. 
ATRYPA ? INCERTA, sp. nov. Pl. XXIV, fig. 30; and Pl. XXV, figs. 7, 8. 
Spec. Char. Obtusely pentagonal, about as broad as long, greatest width posteriorly 
or at about one third of the length of the shell from the beak ; hinge-line straight, a little 
shorter than the width of the shell. Ventral valve either uniformly convex and gibbous, or 
with a broad slightly elevated fold close to the front ; beak tapering to a point, with a 
minute apicial foramen (?); area triangular, about one third as high as long; deltidium 
very wide and flat, with either a narrow longitudinal ridge or line along its centre. Dorsal 
valve not known. Surface smooth. 
Length 10, width 10 lines. 
Obs. Whether this be a distinct species or simply a large variety of Atrypa apiculata 
I am not at present able to determine. Four or five ventral valves only having been 
discovered, it is not possible to offer a complete description of the shell. It differs, how- 
ever, in several particulars from 4. ? apiculata; it is a much larger shell, its hinge-line is 
proportionately longer, and the area and deltidium somewhat different. Under these cir- 
cumstances, and from its being found in a different formation, I have been induced to apply 
to it a distinct specific designation. 
The same difficulty relating to its genus as in the preceding species here prevails ; I 
will consequently leave it provisionally with Aérypa. I am still uncertain whether it 
was provided with an apicial foramen. 
Position and Locality. This species occurs in the Upper Llandovery rocks at Penkill, 
near Girvan, in Ayrshire, where it was discovered for the first time by Mrs. H. Gray, of 
Glasgow. 
