MACROCYCLIS. 89 



expansions like very slij^htly developed subobsolete side cusps. In M. Voyana 

 (PI. I. Fig. D) the central tooth has a lon<i;, narrow, quadranj^ular base of 

 attachment, incurved above, below, and at sides, and bears near its base three 

 small, shar]) cutting points, the median the largest; there seem to be no dis- 

 tinctly developed cusps bearing these cutting points. In M. Duranti (PI. I. 

 Fig. E) the central tooth has a base of attachment somewhat like that of M. 

 Vancouverensis, but longer, and with incurving sides ; the cutting point is the 

 same. I have also examined the lingual membrane of M. sportella (PI. XV. 

 Fig. K), which may be merely a variety of Vancouverensis ; its dentition is 

 quite the same. The other species mentioned above are readily distinguished 

 one from another by the form of their central teeth. 



The side teeth of MacrocycUs at first sight, especially when seen from below, 

 appear to be of the purely aculeate type, as the marginals in Zonites and 

 Limax. From this, one is inclined to consider them all as marginals, and to 

 declare that no true lateral teeth exist, thus making MacrocycUs to agree with 

 Glandina in this particular also. A more careful study shows us that the 

 teeth nearest the median line are modified from the aculeate type, though they 

 do not have the distinct form of the laterals of Zonites, with decided cusps and 

 cutting points. They seem rather to represent those teeth of Zonites which 

 show the transition from the laterals to the marginals (see PI. 11. Fig. F, the 

 second lateral tooth of Z. Icevigatus). It may be said, therefore, that the lat- 

 eral teeth are entirely wanting in MacrocycUs, the first side teeth being laterals 

 in the transition state, the balance being pure marginals. (See, however, 

 M. euspira, Pr. Ac. Nat. Sc. Phila. 1875, PI. XXI. Fig. 3, which has a lingual 

 membrane of Glandina.) The base of attachment of these transition teeth is 

 like those of the marginals, i. e. sole-like, except that the lower lateral expan- 

 sions are more developed and angular, and in concava and Voyana the lower 

 edge is excurved rather than incurved. The cusps are long and slender, 

 lengthened into cutting points ; the teeth are asymmetrical by the greater de- 

 velopment of the outer subobsolete side cusps, both of these cusps being dis- 

 tinctly indicated by expansion. In M. Vancouverensis there is apparently a 

 small sharp side point on the inner side of the cusp. I am not certain of its 

 character, and have not ventured to figure it, excepting on the second tooth in 

 Fig. B of PL 1. This process is seen on the first six teeth only. The balance 

 of the teeth beyond the transition teeth in all the species are marginals of the 

 pure aculeate type. They vary in sharpness in different parts of the same 

 membrane, ns will be seen by comparing my Fig. b of PI. I. Fig. C with the 

 other marginals figuro(L lu M. Duranti the extreme marginals are large in 

 comparison with those of the other species. 



In studying my figures of the lateral teeth, it must be remembered that 

 Figs. C and D are drawn as seen from above, to show the form of the cusp. 

 The other figures are drawn from below, to show the base of attachment. 



M. Vancouverensis, drawn by Morse, has 22 — 1 — 22 teeth, two other mem- 



