Bracatopopa. | LOWER PALASOZOIC MOLLUSGA. 197 
Gonus. SPIRIGERINA (d'O7b.) 
Gen. Char.—Shell oblong, marked with radiating dichotomous ridges; beaks closer, or shewing a 
small round opening close under the beak, separated from the hinge-line by a distinct deltidium of two 
pieces; internally the receiving valve has two short diverging cardinal teeth (one each side of the deltidial 
space) ; the entering valve has a very short mesial septum, and two long apophyses coiled in large flattened 
spires, each nearly parallel with the horizontal plane of the margins of the valves, or a little oblique, so that 
part of the right spire is over the other; in receiving valve the two adductor impressions are very large, 
occupying nearly half the space of the interior ; the pallial trunks are very simple, with few slender branches. 
Most usually, I think, the foramen and deltidium are concealed, but I have myself distinctly seen 
them, and this, as well as the curious nearly horizontal direction of the spires, separates it from the 
others of the family: (for muscular, and other impressions, see S. reticularis). 
SPIRIGERINA? cUNEATA (Dal. Sp.) 
Ref. and Syn.= Terebratula cuneata Dal. Vet. Acad. Verhandl. t. 6. f. 3. Sow. Sil. Syst. t. 12. f. 18. 
Sp.Ch.— Longitudinally trigonal, apical angle 75°, sides long, straight, greatest width at one-third the length 
from the front margin; receiving valve with a nearly straight prominent beak, deeply depressed, to form a wide 
and deep sinus in the front margin; from about two lines from the beak, sides scarcely convex ; entering valve 
with the sides very slightly convex, the two mesial ridges very much elevated from about two lines from the beak, 
forming a prominent mesial ridge towards the front ; each valve coarsely radiated with from twelve to fourteen 
strong, angular, deeply-divided simple ridges, deeply indenting the margin, four of which are elevated with the 
front, but the two middle ones usually more elevated than the lateral pair; an elongate, ovate, concave, smooth 
space, formed by the partial inflection of the posterior lateral margins of the valves, the edge of the receiving 
one forming a very marked rounded lobe, the convexity towards the entering valve, which it thus overlaps con- 
siderably; surface sharply striated transversely by lines of growth. Length six lines, proportional width 
=, depth of both valves (greatest near front margin) =. 
The curious embracing lobe of the sides of the receiving valve has been noticed by Dalman; the long 
straight sides meeting at so small an angle easily distinguish this species from the H. diodonta, to which those 
varieties, in which the two mesial plaits are remarkably prominent, make some approach. I have not been 
able to see the aperture distinctly, nor whether the tissue is certainly fibrous or punctured, so that the generic 
position of the fossil would remain doubtful, as far as my own observation went, but M. d’Orbigny seems to haye 
ascertained the existence of the characters of his genus Spirigerina, in which I accordingly follow him. 
Position and Locality—Not very uncommon in the Wenlock limestone of Wenlock, Shropshire. 
SPIRIGERINA MARGINALIS (Dal. Sp.) 
Ref. and Syn.= Terebratula marginalis Dal. Vet. Acad. t. 6. f. 6. = Terebratula imbricata Sow. Sil. Syst. 
5 2 Sate a2 
Sp. Ch.—Rotundato-quadrate, both valves gently convex, receiving valve least so, mesial hollow deep 
and wide at the margin, continuing with sharp angularly defined sides quite to the beak, which is small, 
prominent, and scarcely incurved; foramen round, separated by a distinctly marked bipartite deltidium from 
the hinge; apical angle 140°; entering valve with the mesial ridge prominent, convex, or slightly flattened, 
very shaiply defined up to the beak; lateral margins nearly level, front margin abruptly raised into a deep 
rotundato-quadrate sinus ; radiating ridges close, angular, branching two or three times from the beak to 
the margin, where, in a specimen eight lines long, there are about seven on the mesial ridge, and eleven on 
each side; at three lines from the beak there are eight on each side, and five on the sinus, all the ridges 
crossed by strong, prominent, scaly lines of growth ; shell-tissue fibrous. Width nine lines, proportional 
length of receiving valve 4, length of entering valve =, depth of both valves jj, (a small cast apparently 
of this species shews the usual oval pit on each side of the beak for the apophyses in the small valve, 
7 
