. Bulletins of American paleontology. ofa continuous series. Shells in which the ribbing is dis-tinct bear from just under 20 ribs per whorl to about25-30 ribs. The rib count for the smooth shells be-gins in the middle thirties and ranges above 40 ribsper whorl. Intermediate shells can be placed in one orthe other species depending on how sharp your eyesare, how well preserved the shell surface is. andwhether the shell has been coated to enhance the ap-pearance of the ribs. The end members are distinctive,but they are connected by an unbroken series of inter-mediate forms. Because there is no
. Bulletins of American paleontology. ofa continuous series. Shells in which the ribbing is dis-tinct bear from just under 20 ribs per whorl to about25-30 ribs. The rib count for the smooth shells be-gins in the middle thirties and ranges above 40 ribsper whorl. Intermediate shells can be placed in one orthe other species depending on how sharp your eyesare, how well preserved the shell surface is. andwhether the shell has been coated to enhance the ap-pearance of the ribs. The end members are distinctive,but they are connected by an unbroken series of inter-mediate forms. Because there is no objective way to break this se-ries of rib counts, we have used only the older namecostata for this taxon. References.—((c) = costata: (s) = scalarifor-mis) Warmke and Abbott, 1961, p. 71, pi. 13, fig. S(c); Morris, 1975, p. 147, pi. 43, fig. 8 (c); p. 147. pi. 43. fig. 7 (s); Abbott. 1974. pp. 103-104. fig. 980 (c); Abbott, 1974, p. 104. fig. 986 (s);Emerson and Jacobson, 1976, p. 82, pi. 20, fig. 17 (c); Bulletin 370. Text-tigure 52.—GastropodsF. TnincaielUi hilahiara. G. EfIl-Yirfii. K. Rissciiia fischfil. ith apertures lacking siphonal notches. A. D. Finc/la ilidiu. B. C. Ceriiliidaiced juvenile of Tnincatella. H. Effaced Tnincarella hilahinla. I. Ribbed juv mdchcllaRtssoiiu Emerson and Jacobson, 1976. p. 82. pi. 20. tig. 18 (s);Rehder, 1981. p. 434, fig. 127 (s); Rehder. 1981. , fig. 124. (c) Tnincatella .52E-1AMOCO Taxon #.—2119 = pukiielUi (); 2120 = hilahiata (Text-fig. 52F); 2483 = bothtaxa combined. Diagnosis.—Shell thin, fragile. The two individualtaxa. shown above, are discriminated by the shape ofthe aperture, which is simple in T. pulchella but bears a strong varix just behind the lip of the shell in In most specimens the surface of piilchelhiis effaced and well-ribbed in bilahiata. but as the ef-faced specimens in Text-figures 52G, H show thatsome bilabiate shells are also effaced so it is impos-s
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