NO. 2250. NEW MARINE SHELLS FROM PAN AM A— BART SCH. 573 



HELIACUS PANAMENSIS, new species. 



Plate 88, figs. 6, 7, 8. 



Shell small, chestnut brown, lenticular. Nuclear whorls well 

 rounded, smooth, separated by a strongly impressed suture. Post- 

 nuclear whorls slightly rounded, marked by spiral cords and axial 

 ribs, the junction of which forms nodules. The first spiral cord 

 forms a shoulder that marks the highest elevation of the whorls. It 

 is situated at some little distance anterior to the suture, which is 

 located in a decidedly impressed groove. Following the nuclear turn, 

 the whorls are sculptured with three spiral cords, of which one marks 

 the summit as indicated, another the periphery, while the third is 

 about midway between the two. As the whorls increase in size three 

 additional cords make their appearance, first as slender threads, then 

 increasing in size until they almost equal the median cord in strength. 

 These three are located between the summit and the median cord. 

 The first of these begins about a half turn behind the beginning of the 

 postnuclear turn, and is situated a little posterior to the middle be- 

 tween the two. The second one begins about one and a fifth turns 

 behind the beginning of the postnuclear turn and is a little nearer to 

 the intercalated cord than the median. The last one has its inception 

 about a half turn behind the aperture, and is about midway between 

 the second intercalated cord and the median one. The axial ribs are 

 well rounded and retractively slanting. There are 24 of these on the 

 first whorl, 35 on the second, and 40 on the remaining half turn, on 

 the latter part of which they are rather closely crowded. The spaces 

 inclosed by the ribs and the spiral cords are well-impressed rhom- 

 boidal pits. Suture strongly channeled. Last whorl rendered keeled 

 by a strong spiral cord, which is covered up in the preceding whorls. 

 This is really the true peripheral cord, but on the preceding turns, 

 the one anterior to it, is the last one visible. 



Base well rounded, openly umbilicated, marked on the anterior half 

 by four equal and equally spaced spiral cords, while the inner half 

 bears three additional spiral cords, of which the one bordering the 

 umbilicus is very broad. The two anterior to this are about twice as 

 strong as the four anterior to these two, and they are also spaced 

 about doubly as wide as the four preceding. Near the aperture a 

 slender spiral thread appears between these two. The axial sculpture 

 of the base is a continuation of the axial ribs on the upper surface, 

 which extend strong and undiminished to the umbilicus. Here, how- 

 ever, we usually have two ribs fused in the cord bordering the um- 

 bilicus with a strong callus between, forming a series of very strong 

 nodules. The junction of the four anterior spiral keels of the base 

 and the axial ribs forms well-rounded nodules, while those of the two 

 succeeding spiral turns are about twice as strong and those of the cord 



