NAPLES FAUNA IN WESTERN NEW YORK, PART 2 229 



us of the presence of prosogyre beaks, but conform in this detail to the rest 

 of the Lunulicardia of the fauna. In Pterochaenia, hereafter discussed, the 

 beaks are unquestionably prosogyre, and this structure is accompanied by 

 other features distinguishing the shells from typical Lunulicardia, princi- 

 pally the broad and horizontally extended flanges of the lunule. In 

 Prochasma, however, the hiatus is bounded by vertical sicae. We can 

 therefore employ the term only with restricted value as a designation for 

 the smooth or finely lined species of Lunulicardium, bearing in mind 

 that in respect to this surface ornament there is every gradation to the 

 conditions represented in Chaenocardiola and Pinnopsis. 



Lunulicardium (Pinnopsis) acutirostrum Hall. 1843 



Plate 1, fig. 1-6; plate 4, fig. 10 



Pinnopsis acutirostra Hall, Geology of New York; report on the fourth 



district. 1843. p. 244, fig. 106, 7 

 Lunulicardium acutirostrum Hall, Preliminary Notice Lamellibranchiata. 



pt 2. 1870. p. 97 

 Lunulicardium ornatum Hall, (partim) Paleontology of New York. 1885. 



v. 5, pt 1, p. 437, pi. 71, fig. 3 o-3'2 



Lunulicardium acutirostrum Clarke, United States Geological Survey. 



Bulletin 16. 1885. p. 62 



In describing some of the Portage fossils, Professor Hall in 1843 



designated two species of Pinnopsis, P. acutirostra and P. ornata. 



These were believed to differ in the acute form and more abundant 



plication of the former, and the much more orbicular form of the latter. 



When, however, these fossils were redescribed and illustrated in 1885, the 



species were united, the former being regarded as an accidental expression 



of the species due to compression or distortion. It was observed that 



" The typical [original] specimen of L. acutirostrum has the anterior 

 and posterior margins abruptly infolded, giving the shell a much narrower 

 aspect than when in its natural condition. The plications are more slender 

 than in the prevailing forms referred to L. ornatum, and from the 

 infolding of the margin those of the posterior end are invisible in the 

 figure [pi. 71, fig. 30]. The specimen, figure 31, subsequently referred 

 to the same species, has a greater proportional hight than the prevailing 

 forms of L. ornatum, the plications are also narrower and with narrower 



