1896.] NATURAL SCIENCES OF PHILADELPHIA. 413 



developed and deposited in the early part of the wet season. The 

 nuclear portion of the shell presents the features so characteristic of 

 many continental Bulimuli in that the first whorl is angulated above 

 and the vertex is consequently concave or even funicular. The sur- 

 face of the nucleus is evenly, closely, transversely ribbed, with fine 

 spiial strife perceptible between the ribs upon magnification. The 

 sculpture of the nuclear whorl merges gradually into that of the 

 succeeding whorls, the ribbing becoming finer until it is lost in the 

 incremental sculpture. The spiral strife become stronger and prac- 

 tically cover the whole shell. Four delicate, fine spiral threads are 

 evenly spaced on the whorls between the periphery and the suture, 

 somewhat broken by the rather regularly spaced incremental eleva- 

 ted lines. Where the two intersect, the epidermis is raised in micro- 

 scopic cilia only visible in finely preserved young specimens. In 

 this condition there are four or five whorls besides the nucleus. 

 They are of a reddish-brown with a pale olive-greenish narrow 

 peripheral band. Up to this point, unless it be that the shell is 

 slightly narrower, the species is indistinguishable from B. unifaseia- 

 tus. About this time, earlier in some later in others, the peculiar 

 indented irregularities of the surface begin to appear ; at first exag- 

 gerated slightly irregular incremental lines, then irregular broken 

 surface markings recalling rusted metal which has been cleaned but 

 preserves the maculse of oxidation. Finally the aperture shows a 

 slightly reflected lip, a pillar thickened, keeled at the base, tubercu- 

 lar with a single tubercle set anywhere along its length ; the outer 

 lip with one or two adjacent tubercles, the umbilicus from large and 

 ample to very contracted, almost closed. 



The peripheral baud persists in some cases; the warty prominen- 

 ces are whiter than the shell normally would be, having a bleached 

 aspect. I should read the developmental history of this species gen- 

 erally as follows : The species sprang from a form not unlike B. 

 Xantudi of Lower California, the superficially more similar Peru- 

 vian B. rhodacvie and pruinosus having a different nucleus. The 

 ova hatching in the height of the rainy season grew normally, and, 

 if the rainy season had been long enough, would have developed into 

 shells with the color and sculpture of B. unifasciatus and the form 

 of a small slender B. jacobi. Some of the specimens almost attain 

 this ideal. Toward the end of the season either occasional hot spells 

 or the influence of salts leached out of the decomposed lava soil by 

 the rains began to effect the growing shells, some more and some less, 



