154 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 39. 



The first of these, Alaba swpralirata Carpenter, is the only shell we 

 have been able to recognize and we very much doubt if any of the 

 other species described in the Mazatlan Catalogue as Alaba belong 

 to this genus. 



In 1905 Doctor Dall described Alaha oldroydi,"- which must be 

 referred to the Rissoina. 



To the above we now add another form, the most abundant on the 

 west coast. 



The drawings accompanying this paper were made by Miss Evelyn 

 G. Mitchell. 



ALABA SUPRALIRATA Carpenter, b 



Alaba supralirata Carpenter, Cat. Maz. Shells, 1856, p. 366. 



Shell elongate-conic, with very strong varices, which form more or 

 less continuous lines over the whorls, semitransparent. Nuclear 

 whorls four, continuing the general outline of the spire with scarcely 



any interruption ; the first smooth; the rest marked 

 by slender, axial riblets of which about forty-two 

 occur upon each of the last two turns. The spaces 

 separating these axial threads are about twice as 

 wide as the threads. In addition to the axial rib- 

 lets the last two turns are marked by a slender, 

 spiral cord about one-third of the distance be- 

 tween the sutures, anterior to the summit. Post- 

 nuclear whorls well rounded, appressed at the 

 summit; the first three smooth; the fourth show- 

 ing fine, irregularly spaced, incised lines, which 

 increase steadily in size on the succeed- 

 ing turns, becoming very pronounced 

 on the last volutions; on the penulti- 

 mate wdiorl there are ten between the 

 summit and the periphery, and these, 

 equally strong, pass over the varices 

 and the spaces between them. In 

 addition to the spiral sculpture, the 

 whorls are marked by conspicuous lines of growth. Suture strongly 

 constricted. Periphery of the last whorl and the moderately long 

 base somewhat inflated and strongly rounded, sculptured like the 



Fig. 1.— Alaba supra- 

 lirata. 



Fig. 2.— Nu- 

 cleus OP 

 alaba su- 

 pralirata. 



oThe Nautilus, vol. 14, 1905, p. 15. 



b In the preparation of the present diagnoses the following terminology is used: 

 ' ' Axial sculpture, ' ' the markings which extend from the summit of the whorls toward 

 the umbilicus. 

 The axial sculpture may be — 



"Vertical," when the markings are in general parallelism with the axis of the shell; 

 " Protract! ve," when the markings slant forward from the preceding suture; 

 "Retractive," when the markings slant backward from the suture; 

 "Spiral sculpture," the markings following the directions of the coils of the whorls. 



