MARCELLU'S LIMESTONES OF LANCASTER 163 



vexity being at about the middle of the shell. Surface marked 

 by three subangular plications on the fold, two in the sinus, and 

 three broad, low plications on the lateral slopes. These are 

 crossed by well marked lines of growth. Plications absent near 

 the beaks and becoming well defined at about one fourth the 

 length of the shell from the beak. A well marked constriction 

 of both valves is often present about half way between the beak 

 and anterior margin. The interior could not be observed. The 

 nearly straight cardinal slopes, elevated ventral beak, and few 

 plications of the fold and sinus are the most characteristic 

 features of the species. 



This species resembles externally Pu'gnax utah of the 

 upper Coal Measures, but the specimens are longer in propor- 

 tion to the width, and the plications become visible nearer the 

 beak than in the latter species. From Camarotoechia (?) 

 duplicata, of the Chemung beds, it differs in the unequal 

 convexity of the valves, straight cardinal slopes, and greater 

 number of lateral plications. This species has been observed in 

 bed VII only at Lancaster, but a similar shell has been found by 

 the writer in material from the Stafford limestone of the Livonia 

 shaft (N. Y. state museum). 



Liorhynchus limitare (Vanuxem) 



Pal. N. Y. 4:356, pi. 56 



There is considerable variation among the shells referred to 

 this species in the different beds of the section. In the shales 

 all the specimens are excessively flattened. In the upper part 

 of bed D, some layers of which are filled with these shells, they 

 are of all sizes from the very young, 2 mm in diameter to those 

 measuring 19 mm in length and 22 mm in width. In the lime- 

 stones they have the normal convexity of the species, and many 

 nearly perfect specimens were found. In bed I the shells are 

 small, the average size being, length 5.5 mm, width 8 mm. In 

 beds II and III, there is a gradual increase in size till in the latter 

 bed the dimensions become, length 12.1 mm, width 15 mm, con- 

 vexity 8 mm. In the uncompressed specimens the plications are 



