. Bulletin of the British Museum (Natural History). PEBASIAN MOLLUSCAN FAUNAS 201. slightly detached from the base of the body whorl, exposing a small umbilicus. Dimensions. In mm. h br hap h/br sa Type of Mesalia ortoni Gabb; 24° Pebas (from Gabb, 1869, h = ;). Lectotype of Hydrobia confusa 26° Boettger; Pebas (from do Greve, 1938: pi. 1, fig. 1). Specimen figured by Boettger 20° (1878) as H. ortoni (from de Greve, 1938: pi. 1, fig. 5). G25291, Pichana. 22° G25292, Pichana. 32° GG21631, Pichana. G
. Bulletin of the British Museum (Natural History). PEBASIAN MOLLUSCAN FAUNAS 201. slightly detached from the base of the body whorl, exposing a small umbilicus. Dimensions. In mm. h br hap h/br sa Type of Mesalia ortoni Gabb; 24° Pebas (from Gabb, 1869, h = ;). Lectotype of Hydrobia confusa 26° Boettger; Pebas (from do Greve, 1938: pi. 1, fig. 1). Specimen figured by Boettger 20° (1878) as H. ortoni (from de Greve, 1938: pi. 1, fig. 5). G25291, Pichana. 22° G25292, Pichana. 32° GG21631, Pichana. G25472, Odostomial of + Woodward (1871) GG19910, Puerto Narifio. 22° GG19911, Puerto Narifio. 22° GG19912, Puerto Narifio. 32° Remarks. One of the specimens figured by Conrad (1871: pi. 10, fig. 13) is of this species but has not been seen and may be lost. The other (NYSM 9253) is of Dyris tricarinata (Boettger). The rich samples from both Pichana and Puerto Narino suggest that Hydrobia confusa Boettger is merely a less aciculate form of ortoni, and, following Parodiz (1969), is placed in synonymy. The two forms nearly always occur together. De Greve (1938) records both Hydrobia ortoni and H. confusa from Iquitos and refigurcd Boettgcr's (1878) material from Pebas. The spire angles measured from de Greve's pi. 1 range from 15° to 19° for H. ortoni and between 28° and 33° for H. confusa: not between 30° 30' and 39° 30' as given in his text. The most acutely spired example of H. ortoni that de Greve figured (1938: pi. 1, fig. 6) has a markedly obtuse apex. D. ortonii may be recognized by its large size and compara- tive smoothness. The spirally sculptured early whorls distin- guish it from the smooth-shelled living Hclcobia and Littoridina,. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may
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