Bracuropopa.] DEVONIAN MOLLUSCA. 377 
and such I have found to be the case in by far the greater number of unpressed specimens, and a few of the 
' smaller specimens (S. calcarata) also shew a slight want of definition in this part, shewing that no distinction 
could be based on this character. When the shell approaches its adult size it becomes the S. gigantea of 
Sowerby and Phillips, without the slightest change of character, so that many of the specimens, both at 
Petherwin and Tintagel could not be referred by a conscientious observer to the one species in preference to the 
other. The character supposed by Phillips to distinguish the S. gigantea from the S. disjuncta, viz. the mesial 
fold being “ indistinctly furrowed or nearly smooth,” is negatived by Mr Sowerby’s original figures, by his type- 
specimens, and the great number of others which I have seen Sowerby has himself suggested the possible 
identity of S. disjwncta and S. gigantea, and Koninck and de Verneuil suspected the union possible of the four 
species here united. 
Position and Locality.—Extremely common in the chloritic slates at Tintagel, Cornwall; and S. Pe- 
therwin, Cornwall, in the slates and subordinate limestone ; slate of Lanlake, Launceston. 
Subgenus. CYRTIA (Dal.) See page 191. 
SPrRIFERA (Cyrtia) HETEROCLITA (Defr. Sp.) 
Syn. and Ref. = Calceola heteroclita Defrance, Dict. Hist. Nat. t. 80. f. 8. 
= Spirifer subconica Sow. Geol. Trans. 2nd Series, Vol. V. t. 57. f. 10. 
Sp. Ch.—Receiving valve pyramidal, height usually two-thirds of the width of the hinge-line, but sometimes 
exceeding it; hinge-line as wide as the shell, cardinal area very large, flat, triangular; entering valve flattened, 
nearly semicircular, lateral margins horizontal, front margin abruptly raised into a yery large angular sinus, from 
which a very wide, deep, angular sinus extends to the beak of the receiving valve, and a large prominent mesial 
ridge extends to the beak of the entering valve; five simple, obtuse, radiating ridges on each side; surface with 
sharp transverse lines of growth. Width seven lines, proportional length of receiving valve = to **, propor- 
tional length of entering valve >, apical angle varying from 90° to 45°. 
I have not clearly seen the characters of the foramen or pseudo-deltidium. Although Defrance figures rather 
fewer lateral ribs, there can be no doubt of the identity of his species with the present fossil, which, on the other 
hand, seems to have no affinity whatever with the carboniferous limestone, C. subconica (Martin), to which Mr 
Sowerby refers it. 
Position and Locality—Common in the limestone of Plymouth. 
Subgenus. MARTINIA (M°Coy). See page 192. 
Martinta Unit (lem. Sp.) 
Ref. and Syn. = Spirifer Urei Flem. Brit. Anim. p. 397; Ure’s Rutherglen, t. 14. f. 12. = Atrypa 
unguiculus Sow. G. 'T. 2nd Series, Vol. V. t. 54. f. 8. 
Sp. Ch.—Subhemispherical, hinge-line considerably shorter than the width of the shell, sides rounded ; 
margins nearly level all round, front usually slightly emarginate in the middle; entering valve slightly convex, 
with a deep narrow sulcus from the beak to the margin; receiving valve very gibbous along the middle, 
gradually sloping to the margins, and with a narrow, deep, mesial sulcus, extending from the beak nearly 
or quite to the front margin; beak very large, tumid, moderately incurved ; cardinal area high, triangular ; 
surface smooth. Average width three and half lines, proportional length of receiving valve =, depth =. 
The internal casts shew traces of a small mesial septum in both valves. 
Position and Locality—Very common in the slates and associated limestone nodules of S. Petherwin. 
[easc, 11.] 30 
