14 PALAEONTOLOGY OF NEW YORK. 



On the basis of the above mentioned peculiarity, ^^ ^^ 



Mr. Dall has separated such forms as L. albida from the " "" ' \ 



genus LiNGtiLA, under the generic term Glottidia,* i. e., 

 shells in which the pedicle-valve bears two diverging 

 parietal ridges and the brachial valve a median ridge 

 of about the same length. Representatives of Mr. 

 Ball's genus have been regarded as confined to liv- 

 ing species,f and as representing the genus Lingula in 

 American seas. Fig_ ,o. pedicievaive. 



Fig. II. Brachial Talve. 



FIGS. 10, 11. 

 Glottidia Palmeri, after Davidson. 



The name Dignomia was proposed in 1871 for certain Devonian and Silurian 

 species, which are characterized by a strong longitudinal septum in "one or 

 both valves."! 



Type, Lingula alveata, Hall, of the Hamilton shales. 



In this species, the median septum is sometimes strong and sharp, sometimes 

 broad and low, with raised margins precisely as in the pedicle-valve of L. 

 anatina (see figures of the species, Plate I). In addition, however, to the 

 median septum, L. alveata, the type species, shows distinct evidence of diverg- 

 ing parietal ridges, and, moreover, is the onXy American fossil species that is 

 known to retain these as a persistent feature. The presence of the longitudinal 

 septum alone in some degree of development, is by no means a rare 

 feature among the palaeozoic species, and, as before observed, specimens fre- 

 quently give evidence of the fact that this has been partially or wholly formed 

 by progressive accretions to the anterior or median muscular fulcra. (See 

 further on this point the observations on the formation of the platform in the 

 Trimerellids.) Thus it has attained different degrees of development in 

 L. quadrata of the Trenton, L. lowensis of the Galena limestone, L. 



* American Journal of Conchology, voL vi, p. 157, pi. viii, &gs. 1-6. 1870. 



t Mr. Davidson calls attention to the close similarity apparent in Glottidia Palmeri, Dall, a,r\iiLi7i.gti,la? 

 Lesmuri, Rouault, in respect to these septal ridg-es. (Brachiopodaof the Budleigli-Salterton Pebble-bed, p. 

 362.) We have just referred to Prof. King's suggestion that the latter species should be placed in a 

 distinct genus, on account of its strong deltidial callosities, apparently adapted for the articulation of the 

 valves, and it will pi'obably prove a i-epresentative of the g-enus Barkoisella (q. v.). 



I Hall, On some Imperfectly known Forms among tlie Brachiopoda. 1871. 



