SCIENCE-GOSSIP. 



75 



lower extremity ; the upper arm at first ascends 

 obliquely, then proceeds horizontally close to the 

 suture, and gradually attenuates. Below these 

 complicated structures, there is a free, thin, hori- 

 zontal fold close to and parallel with the lower 

 suture, and extending from the aperture to a little 

 beyond the lower arm of the bifurcation and its 

 posterior support (see fig. j8e, which shows part 

 of the parietal wall). At the aperture this 

 fold is distinctly united to the transverse sinuous ridge 

 (see fig. j8d). The palatal armature consists of: 

 first, a strong long horizontal fold near the suture 

 and parallel with it, as well as with the posterior 

 portion of the upper arm of the parietal bifurca- 

 tion, with which it terminates at the same point 

 posteriorly ; secondly, a shorter, but much stronger 

 and broader horizontal fold, which deflects with a 



terior half, with the concave side facing the vertical 

 plate (see fig. 78/, enlarged, which shows the inner 

 side of the palatal wall with its folds and denticles). 

 Figs. 78^—1 (also enlarged) show an immature speci- 

 men of five and a-half whorls, in Mr. Ponsonby's 

 collection ; the armature is almost identical with 

 that of the mature specimens, but the main median 

 parietal fold is very short and does not rise from 

 the aperture, while the denticle in front of the lower 

 part of the palatal vertical plate is very strongly 

 developed, and it is united to the plate, so as 

 to form a steep ridge. A second set of barriers, 

 identical in every respect except in being a little 

 smaller, occurs in this specimen one-quarter of 

 a whorl further back. The mature specimen 

 shown in fig. jSd is also in the collection of Mr. 

 Ponsonby, and measures: major diameter, 31 milli- 



Fig. yg.—Plectopylis anguina. 



sharp curve posteriorly, having a little above its 

 posterior termination, and almost in a line with its 

 anterior portion, a slight elongated horizontal 

 denticle ; thirdly, a very short, but strong and 

 broad crescent-shaped fold, deflected at both 

 extremities ; fourthly, facing the concave side of 

 the last-mentioned fold, is a very strong and broad 

 vertical plate, strongly inclined towards the aper- 

 ture, with a much reflexed and thickened edge; 

 this plate intercalates between the two lower arms 

 of the parietal armature ; on the posterior side of 

 the plate and near its lower extremity occurs a 

 stout little denticle, and a little lower and still farther 

 back is found a slight elongated swelling, not 

 amounting to a fold or denticle (yet present in all 

 four mature specimens, as well as in an immature 

 one, examined by me) ; fifthly, a thin horizontal fold, 

 the anterior part straight, but curved in the pos- 



D 



metres ; minor diameter, 24 millimetres ; altitude, 

 9 millimetres ; while the immature specimen 

 measures 17 millimetres in diameter. Three 

 specimens in my collection measure respectively 

 29 : 23 : 9 millimetres, 25 : 20 : 85 millimetres, 

 23 : 18 : 75 millimetres. The types of the species 

 are in the New York State Museum, at Albany, 

 N.Y., and are shown in figs. y8a-c, which are 

 reproduced from the photograph kindly supplied 

 by Dr. Merrill. The following particulars are 

 taken from Dr. Bagg's notes which accompanied 

 the photographs : " Helix repercussa, Gould. Bur- 

 mah. Catalogue No., 236; original No., A 564. 

 Major diameter, ij inch [= 28-5 millimetres]; 

 minor diameter, J inch [=22 millimetres] ; alti- 

 tude, ^ inch [=8 millimetres] ; greatest diameter 

 of aperture, ^ inch [= 11 millimetres]." Dr. 

 Gould states that the species was taken in the 



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