113 



this form, I should be disposed to regard this as the typical form of C. frondosa (Hall). In 

 such examples of C. frondosa, 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 C. 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. intertexta and the two forms included under Hall's C. 

 frondosa, I 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 C. frondosa (Hall), should be restricted to the forms with the very small fenestrae 

 (Pal. N. Y., Vol. II , PI. XL., B., fig. 56.), whilst the name of C. intertexta 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 Ptilodictyce. 



Locality and Formation. Corniferous Limestone of Jarvis, Township of Walpole. 

 (Collected by Mr. George Jennings Hinde). 



CHAPTER V. 



LAMELLIBRANCHIATA PTEROPODA, AND GASTEROPODA 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., 

 Vanuxcmia 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). 



Pkurorhynchus trigonalis (Hall), Rep. 4th Geol., Dist. New York, p. 272, figs. 6a, 6b., 

 (not Pleurorhynchus trigonalis, Phillips). 



Conocardium sub-trigonale (D Orbigny), Prodr., Vol. I., p. 80. 



Conocardium trigonale (Meek), Gological Survey of Ohio, Palaeontology, 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, urnbo- 

 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 of a 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 inclination. 

 Surface ornamented by simple, regular, radiating costae, separated by furrows of about the 

 same size or less ; costaj smaller and more crowded on the anterior flattened t'aee 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 



