278 PROCEEDINGS OF THE ACADEMY OF [1889. 



27. The rhachidian tooth (fig. e, r) is small, narrow, subulate, with 

 well -developed cusp. Its base differs in form from the correspond- 

 ing part in Streptaxidce, Oleacinidce, or Selenitidce, being produced 

 into two slender diverging branches. The lateral teeth are all of 

 purely 'aculeate' form, and increase in size from the first to the 

 twelfth, which is enormously developed. The teeth lying outside of 

 the twelfth are apparently functionless ; they are minute, and 

 decrease in size rapidly toward the outer edge of the radula. All of 

 the teeth have distinct basal-plates. The cusps seem simply sabre- 

 shaped when lying in a natural position ; in figure F, I have drawn 

 the third, fourth and fifth teeth seen partly in profile. The affinities . 

 of the genus seem to be with Rhytida, judging from the characters 

 of the radula, differing from that genus in the retention of a well- 

 developed rhachidian tooth. * A complete half-row of teeth is shown 

 in figure e. 



The genitalia (PI. ix, fig. g) present no characters unusual in the 

 Agnatha, bearing a closer resemblance to those of Glandina than to 

 any other form known to me. Like Glandina the penis is rather 

 slender, the vas deferens inserted at its apex, and forming a 

 continuation of the former organ. The ovotestis is formed of a com- 

 pact mass of club-shaped ccecre about thirty-five in number. The 

 hermaphrodite duct is considerably convoluted and short between 

 the ovotestis and the albumen gland. Its lower portion ( " vagina ") 

 is convoluted or twisted several times upon itself. The duct of the 

 spermatheca (again as in Glandina) is very long, inserted high upon 

 the oviduct, and terminates in a small oval receptaculum seminis. 

 The genital orifice is very near the head. 



ZINGIS, von Martens. 



Zingis was proposed for a South African Naninoid species with 

 the following characters: "shell heliciform with simple peristome; 

 hinder extremity of the foot with mucous pore and a little prom- 

 inence above it ; jaw smooth, with median projection ; marginal teeth 

 of the radula bicuspidate." Type, Z. radiolata Mart., from near 



* See Hutton, Trans. New Zealand Institute, xvi, p. 167, pi. 10, figs, 

 s, R, Q. for dentition of Rhylida. Also Binney, Annals N. Y. Acad. Sciences 

 iii, p. 82, pi. xvii, fig. l. 



In the form of the central tooth, Aerope Knysnaetisis seems to be nearest to 

 certain species of Glandina. See Fischer et Crosse, Moll. Mex. et l'Amer. Cent., 

 pi. 4, fig. 10 (G. algira). Other species of Glandina have simply a narrow basal 

 plate, without cusp. From all Slreptaxida, Aerope differs in possessing distinct 

 basal plates to all of the teeth. 



