Raymond: HRAciiioronA and Ostracoda ok the Chazy. 221 



cast (it tlu' lir.u'lii.il \.il\r, tlu-iu is a narrow ritl^e as there is in similar 

 casts of Cainarotivcliia congrcgala. Tiiis ri(ii;o indicates that the se])liiiii 

 di\itle(l at tlie posterior end. In Rhyiuhotrcma capax this ridge is 

 di\i(k'd l)\ a dee]) and narrow cleft, indicatinj^ the cardinal process, 

 but in the casts of Rliynclionclla oriciilalis there is no sign of such a 

 cleft, and the ridge is smooth, as in Camarolcechia congregata. In 

 Professor Hudson's collection there are casts of the interior of Cama- 

 rolcechia pristina Raymond which show this same condition, and in 

 the Carnegie Museum there are two internal casts of Rhynchonella 

 plena llall which show the undi\ided ridgi- at the posterior end of the 

 furrow made by the dorsal septum. If then, the separation of these 

 genera depends upon the presence or absence of the cardinal process, 

 as it seems to do, all three of the common rhynchonelloids of the Chazy 

 must be referred to Camarota^chia. The interior of Camarolcechia 

 major is not known. 



6. Camarotcechia plena Hall. 



(Plate XXXIII, figures 7-18.) 

 Atrypa plena Hall, 1847. Paleontology of New York, \'ol. I, p. 21, PI. 4 bis. 



figs. 7a-7'^- 

 Atrypa plicifera Hall, 1847. Ibidem, p. 22, PI. 4 bis, figs. 8a-8(i. 

 Alrypa allilis Hall, 1847. Ibidem, p. 23, PI. 4 bis, figs, ga-gd. 

 Atrypa plena Billings, 1856. Canadian Naturalist and Geologist, Vol. I, p. 208, 



figs. 17, 18, Pig. 

 Atrypa plena KOGEKS, 1858. Geologj' of Pennsylvania, Vol. H, pt. 2, p. 817, fig. 592. 

 Rhynchonella plena, plicifera, allilis Hall, 1859. 12th Annual Report New York 



State Cabinet Natural History, pp. 65, 66. 

 Rhynchonella plena Billings, 1859. Canadian Naturalist and Geologist, Vol. I\', 



p. 444. fig- 22. 

 Rhynchonella plena Billings, 1863. Geology of Canada, p. 126, fig. 50. 

 Camarolcechia plena and allilis H.\ll and Clarke, 1893. Paleontology of New York, 



Vol. VIII, pt. 2, p. 190. 



Camarolcechia plena is the most abundant and probably the most 

 variable of the fossils of the Chazy. With a large quantity of material 

 at hand; it becomes a difficult matter to determine whether or not some 

 of the extreme variations should receive sjjccific names. 



A study of the shells in all stages of growth shows that the three 

 species described by Hail must be combined as one species. Atrypa 

 plena and Atrypa plicifera represent the normal adult, and Atrypa 

 allilis the extreme stage to which dexelopment in the number of pli- 

 cations can be carried. 



