PACIFIC COAST SPECIES. 81 



the laterals of Zonifes, with decided cnsps and cutting points. They 

 seem rather to represent those teeth of Zonites which show the transi- 

 tion from the laterals to the marginals (see Terr. Moll., V, Plate II, 

 Fig. F, the second lateral tooth of Z. laivigatus). It may be said, there- 

 fore, that the lateral teeth are entirely wanting in MaerocycUs, the first 

 side teeth being laterals in the transition state, the balance being pure 

 marginals. (See, however, M. euspira, Ann. IST. Y. Ac. Nat. Sc. II, Plate 

 II, Fig. I, which has a lingual membrane of Glandina.) The base of 

 attachment of these transition teeth is like those of the marginals, *. e., 

 sole-like, except that the lower lateral expansions 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 development 

 of the outer subobsolete side cusps, both of these cusps being distinctly 

 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 Plate I of T. M. V., and also wood-cut below. 

 Fig. 45. 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, as will be seen by comparing my Fig. b of Plate 

 I, Fig. C, with the other marginals figured. In M. Duranfi the extreme 

 marginals aie 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. Vancouveremis, drawn by Morse, has 22-1-22 teeth ; two other 

 membranes examined by me gave 24-1-24, one other 18-1-18. M. con- 

 cava has given 20-1-20, 23-1-23, and 25-1-25. Of M. Duranti I have 

 counted but one membrane having 18-1-18. A single membrane of i¥. 

 Toy ana had 24-1-24 teeth. M. sportella has 22-1-22. 



To sum up the characters of the dentition of MaerocycUs, it may be 



said to be intermediate between Glandina and Zonites, difiering from 



the former in the presence of the transition teeth from true laterals 



to true marginals, differing, however, from the latter by the absence of 



true lateral teeth. 



Baudonia being preoccupied. Dr. Fischer suggests the name Selenites 

 1749— Bull. 28 G 



