578 T2E PALEONTOLOGY OF MINNESOTA. mucuUda!. 



.Family NUCULID^. 

 aenus CTENODONTA, Salter. 



Nucula, Hall, 1843. Geol. Eep. Fourth Dist. N. Y., p. 76; Amer. Jour. Sci., vol. xlviii, p. 292; 



1847, Pal. N. Y., vol. 1, pp. 150 and 316. 

 Lgrodesma (part.), Hall, 1847. Pal. N. Y., vol. 1, p. 302. 

 TelUnomya, 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 TelUnomya, the correct form of Tellimya, Beown, 1827, as given 



by Agassiz in 1846 in his "Nomenclator Zoologicus.") 

 Otenodonta, Salter, 1851. Rep. Brit. Assoc.,, p. 36; 1859, Can. Org. Rem., Decade i, p. 34. 

 Palceoconcha, S. A. Millek, "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. {TelUnomya) nasuta Hall. 



Several reasons. have operated in the rejection of Hall's earlier name TelUnomya 

 in favor of Salter's Ctenodonta. First among these is the fact that TelUnomya 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, I 

 am obliged to hold that TelUnomya, Hall, cannot stand under the rule relating to- 



*It is quite difficult to estaWlsh which Is the anterior end In these shells. For the sake of unitormlty I have, in 

 each case, assumed that the higher end (it is usually also the rounder) is the anterior. It may he well to state, moreover, 

 that I am not at all satisfied that this rule should apply in the C. recuroa section of the genus, nor that Salter, Meek and 

 Worthen, Hall and others who have described species ol that section, are right In assuming that the sifle toward which 

 the beaks are turned is the posterior. Though I have followed these authorities, I have done so chiefly because it seemed 

 desirable, at any rate until the genus was worked up monographically, to have our descriptions as uniform as posstole. 

 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 really a fact is, I believe, conclusively shown in C. rwuroa. (See plate xm, fig. 101.) 



