113 
ee tm 
this form, I should be disposed to regard this as the typical form of C. frondosa (Hall). In 
such examples of C. frondosq, further, as I have examined, the cells are remarkably long and 
narrow, and about fourteen of them occupy the space of one line measured transversely ; 
whereas, in (’. intertexta the cells have a sub-quadate or rounded form, with nearly circular 
mouths, and only six to eight of them occupy a line transversely. In spite, therefore, of the 
close general resemblance between C. interteata and the two forms included under Hall’s (. 
frondosa, 1 am inclined to think C. intertexta to be specifically’ distinct. If this should subse- 
quently, by a comparison of specimens, be proved not to be the case, I should propose that 
the name of (. frondosa (Hall), should be restricted to the forms with the very small fenestrze 
(Pal. N. Y., Vol. IL, Pl. XL., B., fig. 5.), whilst the name of C. interteata should be applied 
to the undoubtedly distinct forms with large fenestrae. In any case, as before remarked, both 
of these species of Clathropora might, without impropriety, be looked upon as nothing more 
than reticulated Ptilodictye. 
Locality and Formation.—Corniferous Limestone of Jarvis, Township of Walpole. 
(Collected by Mr. George Jennings Hinde). 
CHAPTER. V. 
LAMELLIBRANCHIATA PTEROPODA, AND GASTERQPODA—OF THE CRNIFEROUS AND 
HAMILTON FORMATIONS. 
LAMELLIBRANCHIATA, 
Mr. Billings states, that he has met with about twenty species of Lamellibranchiata in 
the Corniferous Limestone of Western Ontario, and of these he names and describes one, viz., 
Vanuaxemia Tomkinsi (Canadian Journal, New Series, Vol. VI., p. 357). This species I have 
not seen, and the only Lamellibranch which I have met with, either in the Corniferous Lime- 
stone or the Hamilton group, is the well-known Conocardium trigonale (Hall). 
136. CoNoCARDIUM TRIGONALE (Hall). 
Pleurorhynchus trigonalis (Hall), Rep. 4th Geol., Dist. New York, p. 272, figs. 6a, 66., 
(not Plewrorhynchus trigonalis, Phillips). 
Conocardium sub-trigonale (D’Orbigny), Prodr., Vol. I., p. 80. 
Conocardium trigonale (Meek), Gological Survey of Ohio, Palaontology, Vol. I., p. 201- 
Shell trigonal, with the anterior extremity distinctly cordate. ‘ Anterior side abruptly 
truncated, with a forward slope from the beaks to the more or less angular anterior basal 
extremity, and flattened, or sometimes even a little concave, near the outer margins, so as to 
meet the lateral surfaces at about right angles, or less, along the prominent, angular, umbo- 
nal slopes, which extend to the anterior basal extremity, and are produced forward in the 
form of a peculiar thin alation, that is most extended below ; dorsal margin behind the beaks 
nearly straight and horizontal, or a little declining and slightly concave in outline with the 
edges of the valves incurved, while in front of the beaks it is more or less produced forward 
in the form ofa narrow (beak-like ?) extension ; basal margins of the valves strongly incurved 
and distinctly crenate within, nearly straight in outline, anteriorly and obliquely ascend- 
ing, with a more or less convex outline posteriorly to near the hinge, below which they 
are widely gaping so as to form an ovate or sub-cordate hiatus, and present a slightly sinuous 
outline ; posterior extremity (when not broken or worn away) distinctly angular at the ter- 
mination of the hinge-line above; beaks moderately prominent, gibbous, and distinctly 
incurved nearly at right angles to the hinge, or with a very slight backward ‘inclinatiov. 
Surface ornamented by simple, regular, radiating costa, separated by furrows of about the 
same size or less ; costze smaller and more crowded on the anterior flattened face of the valves 
than on the flanks behind the umbonal angle, and not defined on the anterior umbonal ala- 
tion ; crossing all of these markings, there are numerous fine, regular, crowded, concentric 
8 
