TRANSACTIONS OF WAGNER 

 6i6 



TERTIARY FAUNA OF FLORIDA 



parallel with the hinge-line. Consequently, it may follow that in the process 

 of growth the same individual may at an early stage have a series of vertical 

 median denticles, and at a later stage may pesent a hiatus destitute of teeth 

 between the anterior and posterior parts of the series. Judging from the 

 species I have been able to examine, the entire narrow cardinal area is orig- 

 inally covered by the ligament, but the grooves containing the resilium extend 

 very obliquely backward from the beaks, as in typical Acar. Notwithstanding 

 the resemblance of the hinge in these Tertiary and recent .species to that of 

 the Paleozoic and early Mesozoic Parallelodon, I am of the opinion that the 

 relations of the former are really closer with the true Arks, and that the 

 similarities will prove to be analogical rather than homologous. The recent 

 abyssal species I have formerly referred to Macrodoii should probably be 

 grouped under CitaiUaria. 



Verrill has recently proposed to separate generically the above-mentioned 

 recent species from forms like A. hctcrodonta Desk., the type of CuciiUaria, 

 and to call them Bentharca. The degree of inclination of the anterior teeth 

 in these shells is hardly more than a specific character in my opinion, differing 

 but slightly between many of the species, though the extremes of the series, 

 taken alone, differ widely. 



Group of A. ritbrofiisca Smith [Lissarca Smith, 1876). 



Umbones nearly terminal, equivalve, hinge-line arched with an edentulous 

 hiatus in the middle, sculpture concentric, area lineal, with a central very small 

 ligament. This occupies to Barbaiia much such a relation as Bathyarca does 

 to Scapharca. 



Group of A. tortuosa L. {Trisidos Bolten, 1798, -f Trisis Oken, 1815). 



A small group of thin shells with a long, straight hinge-line and many small 

 similar teeth, the valves more or less spirally twisted. The latter character is 

 not particularly valuable in classification, but the group is easily recognized. 

 Group of A. celox Benson [Scaphida Benson, 1835, not of Swainson, 1840; 



Scapliiira Gray, 1847, ^Y typographical error). 



Small, keeled, smooth externally, inhabiting Indian River. The soft 

 parts do not appear to have been studied. 



Subgenus NOETIA Gray. 

 Noetia Gra.y, Syn. Cont. Brit. Mus., 1840; Agassiz Nomenclator, Molliisca, 1842. Type 

 Area reversa Gray. 



