575 THE PALEONTOLOGY OF MINNESOTA. eae 
LNuculide. 
Family NUCULID.. 
Genus CTENODONTA, Salter. 
Nucula, HALL, 1843. Geol. Rep. Fourth Dist. N. Y., p. 76; Amer. Jour. Sci., vol. xLvin, p. 292; 
1847, Pal. N. Y., vol. 1, pp. 150 and 316. 
Lyrodesma (part.), HALL, 1847. Pal. N. Y., vol. 1, p. 302. 
Tellinomya, HALL, 1847. Pal. N. Y., vol. 1, p. 151; 1857, Tenth Ann. Rep. Reg. Univ. N. Y., p. 181: 
also of the majority of American paleontologists since that date. 
(Not Tellinomya, the correct form of Tellimya, BROWN, 1827, as given 
by AGASsIz in 1846 in his ‘‘ Nomenclator Zoologicus.’’) 
Ctenodonta, SALTER, 1851. Rep. Brit. Assoc., p. 36; 1859, Can. Org. Rem., Decade i, p. 34. 
Palewoconcha, 8S. A. MILLER, 1889. North Amer, Geol. and Pal., p. 498. 
Shell equivalve, closed, usually largest anteriorly,* occasionally subequilateral, 
with the beaks situated sometimes behind the middle, but usually more or less in 
front of that point; surface marked by concentric lines of growth; beaks approxi- 
mate, generally small and never very prominent. Ligament external, rather small, 
situated immediately behind the beaks; no striated area nor internal cartilage pit. 
Hinge more or less arcuate, sometimes very gently, at other times bent almost at a 
right angle; with series of small curved or geniculated transverse teeth, which 
diminish in size more or less gradually from the extremities to the beaks; the 
series are continuous and gradually pass into each other in the typical section of 
the genus, but in other sections they are often interrupted beneath the beaks. 
Adductor muscular impressions two in each valve, subequal, nearly always readily 
distinguishable, and sometimes very deeply impressed, situated just beneath the 
anterior and posterior extremities of the hinge; scars of small foot-muscles have 
been observed in a number of species, one immediately above or in front of each of 
the adductor scars; pallial line indistinct, simple, submarginal. 
Type: C. (Tellinomya) nasuta Hall. 
Several reasons have operated in the rejection of Hall’s earlier name Tellinomya 
in favor of Salter’s Ctenodonta. First among these is the fact that Tellinomya was 
used for a totally different group of shells at least one year previous to the date of 
publication of the first volume of Hall’s Paleontology of the state of New York, 
namely, in 1846 by Agassiz, in his “Nomenclator Zoologicus,” when he catalogued 
the correct form of the incorrectly constructed generic name Tellimya, which had 
been proposed by Brown in 1827. Believing that such corrections are allowable, | 
am obliged to hold that Tellinomya, Hall, cannot stand under the rule relating to 
*It is quite difficult to establish which is the anterior end in these shells. For the sake of uniformity I have, in 
each case, assumed that the higher end (it is usually also the rounder) is the anterior. It may be well to state, moreover, 
that I am not at all satisfied that this rule should apply in the C. recurva section of the genus, nor that Salter, Meek and 
Worthen, Hall and others who have described species of that section, are right in assuming that the side toward which 
the beaks are turned is the posterior. Though I have followed these authorities, I have done so chiefly bee: wuse it seemed 
desirable, at any rate until the genus was worked up monographieally, to bave our descriptions as uniform as possiple. 
Had I followed my own inclination it would have been to reverse, in this case, the present application of anterior and 
posterior, upon the ground that the external ligament was situated upon the covex half of the hinge instead of the con- 
cave, That this is reaily a fact is, I believe, conclusively shown in C. recurva. (See plate xnar, fig. 101.) 
