Originally: Modiolopsis cincinnatiensis
[leaflet-map lat=39 lng=-84.5 zoom=7 width=575 height=250 align="right"]
Map point data provided by iDigBio.
- C3 Sequence (Corryville)
Identification in Hand Sample
Whiteavesia cincinnatiensis from the Trenton Group (CMC 61657)
Pojeta, Jr. (1971):
- Whiteavesia cincinnatiensis is entirely edentulous.
- The type of this genus is the Modiolopsis cincinnatiensis, Hall and Whitfield, described in the second paleontological report of this survey. It is a common and highly characteristic fossil of the lower fifty feet of the Cincinnati group. The figures given by the authors of the species on plate II of the work cited, do not, according to my observation, correctly represent the species. During the past eighteen years, I have had opportunities to examine an aggregate of several hundred specimens, most of them in an unusually good state of preservation, and all of them bearing evidence for the great constancy of the specific characters of the form. None, so far as I can remember, could be said to approach even the figures given by Hall and Whitfield in the angularity of the posterior extremity.
- Figure 16 on plate 56 of this report, represents a well-preserved cast of the interior of a large right valve. It shows beside the normal form of the shell, the merely outlined anterior muscular scar, obscure traces of the posterior scar, and radial lines on the ventral slope. The latter, as is the case also with other species of the genus, never show on the exterior of the shell but are strictly an internal feature and rarely noticeable except on well grown or old samples.
- Associated with this species, at any rate with the shell that every collector at Cincinnati has identified with Hall and Whitfield’s M. cincinnatiensis, another is found, though much more rarely, which may have been included by them in their M. cincinnatiensis and perhaps used in the illustration of their species. The posterior end of this shell has an outline really very much like their figure 14. Being subangular at the end of the hinge and but little curved in the oblique slope from that point to the sharply rounded post-basal angle. While I can believe readily that specimens of this second form may have been included among those to which they applied the name cincinnatienesis, I cannot understand, considering the attention they were obliged to give it in making a drawing of it, how they could have failed to notice the radiating lines which traverse the cardinal and posterior parts of the surface and are distinguishable even on all the internal casts seen by me. Such radii are not often to be seen in the common form, but it is important to know that they do exist occasionally, though always fainter than in the rare one.
- This genus brings into very natural association a number of Lower Silurian species, the described forms of which have heretofore been placed chiefly with Modiolopsis. These are Modiolopsis cincinnatiensis H. and W., M. cancellata Walcott, M. pulchella Ulrich, and two undescribed species from the lower or Utica horizon of the Cincinnati group, A. subcarinata, n. sp., from the Galena, and Modiolopsis superba Hall, M. modioliformis Meek and Worthen, and Orthodesma saffordi Ulrich, from the lower limestone of the Trenton formation.
- Besides these, I propose to place here another group of species, go far known only from rocks above the Trenton, that approaches Modiolopsis in the strength and definition of the anterior adductor impression, while differing from that genus, and therein giving us a clue to their origin, in the convexity of the basal outline and absence of a mesial depression or so-called “byssal sulcus,” and in the character of the hinge, which is thinner, and thus more like that of an Orthodesma than of species of Modiolopsis of the same size. Four species of this kind, all from the Cincinnati rocks, are known to me, only two of them, however, being described, i.e., Modiolopsis pholadiformis Hall, and M. oblonga Ulrich.
- The systematic position of Actinomya seems to be nearly intermediate between Orthodesma and Modiolopsis, differing from the former in the somewhat shorter form and tightly closing instead of gaping valves, from the latter in the thinner hinge plate and shell and both in the convex basal outline and absence of a mesial sulcus.