xxviii SYNOPSIS OF GENERA. 



or by several oblique teeth* Ligament external, contained in a shallow and 

 narrow groove along the cardinal border Muscular scars not strongly impres- 

 sed, situated below the extremities of the hinge-line. Pallial line simple. 



This genus differs materially from Nucula, Leda and Yoldia, in the absence of 

 a cartilage-pit beneath the beaks ; in having an external ligament and a sulcus 

 on the post-umbonal slope. It differs from Nuculites in form, and in the absence 

 of a clavicular ridge on the anterior end. In general form and internal char- 

 acters this genus very closely resembles Tellinomya, and it is probable that 

 further study will prove that the two are congeneric. 



Examples : Palaoneilo constrida, pi. xlviii, figs. 1-16. 



Palaoneilo fecunda, pi. xlix, figs. 13, 15-24. 

 PaUumeilo attenuala, pi. 1, figs, 34-39. 



Macrodon, Lycett (Murch. Geol. Chelt.). 



Shell equivalve, inequilateral, transverse, sub-elliptical, or sub-ovate in out- 

 line. Anterior end angular at the cardinal line, rounded below. Posterior 

 end rounded or obliquely sub-truncate. Beaks anterior to the middle. Cardinal 

 line long and straight. 



Surface marked by concentric striae which are often regularly laminose, and 

 in some species by fine radiating striae. 



Hinge furni.shed with several (sometimes eight) small diverging teeth beneath 

 the beak and by from two to four lateral teeth situated near the posterior ex- 

 tremity of the cardinal line. Ligament external. Muscular impressions not 

 strongly marked. Pallial line simple. 



Examples : Macrodon Hamiltonia, pi. li, figs. 1-7, 9, 10. 

 Macrodon Chemungemis, pi. li, figs. 11-16, 



 The hing'e chai-acters of this gfenus and the resemblance to the genus Neilo were firat indicated to me 

 by Mr. R. V. Whitfield. 



