52 SYEIAN MOLLUSCAN FOSSILS. 



Gonodon ? hebes, sp. nov. 



Plate IV, flss. 1 a, b, c, d. 



Testa suhqiiadrata, veniricosa, crassiuscula, jmuhim inceqidlatera, rurjulls incre- 

 menii modicis irreffuluribus ohducta : latus aiiticiuu im'hrvve, iruncaiim rotundatum, 

 posiicmn longius, altum, rotundato-angidatum, fere vcriicaUler iruiiccdiim : wnbones 

 anieincdiani, tiirgidi, return, incurvi : lunula nulla aut parva et ilUmitata: specimi- 

 nis iinici umhonum cacumina absumpta ; area ligamentalls cardiimque pais magna 

 exesoi : idnusquc valvm dens cardlnalis anitcus trigomis, robustus, latus, superne pro- 

 funda concaviis ; margines iiitus Iceves. CetercB notoi cerni non possunt. 



Shell subquadrate, ventricose, moderately thick, somewhat inequilateral, 

 covered with irregular wrinkles of growth of inconsiderable size : anterior 

 side very short, truncately rounded, hinder side the longer, high, obliquely 

 angled by an obscure rounded umbonal ridge, almost verticaly truncated : 

 umbones antemesial, swollen, blunt, incurved : lunule none or small and 

 undefined : tips of imibones of the single specimen decayed ; ligamentary 

 area and larger part of the hinge removed by corrosion ; under the beak of 

 each valve a wide, strong triangular tooth, deeply concave above and pro- 

 longed in the direction of the longitudinal axis of the shell. The other 

 characteristic marks cannot be distinguished. 



Single specimen, with test. Length, 37 nun. ; height, 34 mm. ; thickness, 

 28i mm. 



Of the solitary example, the beaks in part, the whole area, and the greater 

 portion of the hinge have been removed by decay. Beneath the beak in 

 each valve remains a remarkably prominent triangular tooth, deeply hol- 

 lowed upon its inwardly sloping wide upper face. These teeth are quite 

 unlike any others of which I have knowledge, and it is difficult to give a 

 correct idea of them either by a figure or in words. 



The peculiar form, together with the concentrically wrinkled surface and 

 the somewhat enlarged lunular margin, indicates the relationship of this shell 

 to that group of the Luclnidce to which the genus Unicardiuni belongs. The 

 abnormal development of the two remaining hinge-teeth forbids that it 

 should be referred to any genus of that group except Gonodon. Since the 

 work* which contains Schafhanitl's original diagnosis of that genus is want- 

 ing in the libraries of Cambridge and Boston, I have it only as given by 



* Slid-Bayerus Letlisca Geognostica, 1SG3. 



