78 PALEONTOLOGY OF NEW YORK. 



The opposite viilve sliows the very peculiar feature mentioned by Mr. 

 Billings, a thickened area in the umbonal region presenting the appearance of 

 a false cardinal area inside the cavity of the umbo, a character which is sug- 

 o-estive of that in Lingulasma, but evidently of different function. This area 

 is tripartite, bearing a deep, narrow central and two broader lateral grooves ; 

 about its anterior margin lie two broad scars of the same character as the 

 laterals of the other valve. There are also seen the diverging furrows, which, 

 starting at the marginal apex, pass over the edge of the thickened area, and 

 are most deeply impressed at their anterior extremities. 



To homologize the muscular features seen in Elkania with those of Obolella 

 or any allied genus, is a difficult matter. Mr. Ford was disposed to regard the 

 central depression of the pedicle-valve as an extravagant development of the 

 pedicle-pit seen in 0. crassa and 0. chromaUca. This appears very plausible, 

 but complicates the correspondence of the other scars ; and, moreover, as the 

 internal .'^cars of the opposite valves do not essentially differ in their number 

 and arrangement, it would compel the assumption of a pedicle-pit in the 

 brachial valve. Mr. Foru has suggested that Walcott's species, Obolella ? am- 

 bigua* i'rom the " Pogonip group " of Nevada, is congeneric with E. desiderata. 

 Mr. Walcott's figures, 2 a, 2e, of the interior of the pedicle-valve, indicate the 

 unquestionable correctness of this reference. 



Genus PATERULA, Barrande. 1879. 



PLATE IV K, FIG. 1. 



1S79. Paterttla, BABRiNDii. Rysteme Sihiiien du Centre do la Boheme, voL v. p. 110, pi. 95, fig.'!, i, 



1-3 ; 1)1. 15-J, figs, i, 1-9. 

 1884. Paterula, Davidson. General Summary to Bi'itish Fossil Bi-aehioiKida, p. 391. 



Diagnosis. "Les deux valves, circulaires ou faiblement ovalaires, ne pre- 

 sentent qu'un bombement tres pen prononcr vers I'exterieur. L'espace interne 

 devait done t'tre tres exigu. 



" Ces deux valves se rencontrent habituellement isolees. Cependant, nous 

 figurons PI. 152, deux specimens de valves juxtaposees, qui paraissent avoir 

 appartenu a un meme individu. Nous pouvons ainsi constater, qu'il n'existe 



* Palaeontology Eureka District, }>. 67, pi. i, fig. 2. 



