Iddings and Penfield — Fayalite in Obsidian of Lipari. 75 



arcuate first septum, and that the second is comparable with 

 the third or fourth of T. uniangulare, clearly indicating that 

 the development has been accelerated by the skipping of at 

 least two phases of growth in the septa. In other characters, 

 the two forms merely indicate differences which are probably 

 only of specific importance, such as the more angular form of 

 the lobes and saddles in T. retrorsum, var. typum, and the 

 absence of the minute cone at the summit of the annular lobe. 

 Tale University Museum, April, 1890. 



EXPLANATION OP PLATE I. 



Figure 1. — Protoconch, showing first septum with lateral edges broken, x 18. 



Figure 2. — Side view of preceding, x 18. 



Figure 3. — Ventral view of protoconch with one attached air chamber, showing 

 siphonal ccecum. x 18. 



Figure 4. — Side view of first whorl, x 18. 



Figure 5. — Ventral view of preceding, showing development of ventral lobe, x 1 8. 



Figure 6. — Transverse section of two whorls near the protoconch. x 18. 



Figure 7. — Ventral side of protoconch, retaining the shell, x 18. 



Figure 8. — Ventral side of specimen with first chamber, showing surface orna- 

 ments and indication of siphonal ccecum. x 18. 



Figure 9. — Profile of same, x 18. 



Figure 10. — Surface ornaments on a specimen consisting of a single whorl, x 18. 



Figure 11. — Four strias from the second whorl of a specimen showing funnel 

 sinus, x 18. 



Figure 12. — Vertical section showing septa and air chambers. x 18. 



Figure 13. — Outline of a half grown specimen, x 3. 



Figure 14. — A series of developed septa beginning with the first, showing gradual 



inception and formation of lobes and saddles to the adult period 



represented byj. a, b, c, d, represent the 1st, 2d, 3d and 4th septa, 



while e and / represent the 7th and 8th respectively, x 9. 



Specimens in Yale University Museum, from the Hamilton shales of Wende 



Station, N. Y., except specimen figure 13, which is from 18-Mile Creek, N. Y. 



Art. IX. — Fayalite in the Obsidian of Lipari / by Jos. 

 P. Iddings and S. L. Penfield. 



The Lipari islands have long been celebrated for their acid 

 lavas and pumices ; and it was for the purpose of becoming 

 acquainted with their craters and flows of these rocks that one 

 of the writers recently visited this far famed locality. The 

 obsidian flows that terminated the volcanic activity which built 

 up the craters of snow-white pumice stretch their glassy 

 streams down the steep mountain slopes into the sea. Their 

 upper surface presents a rough and forbidding tract of sharp 

 angular blocks, which appear to have suffered very little change 

 since the solidification of the lava. This portion of the ob- 

 sidian is filled with small gas bubbles that give it a gray color, 

 and a more or less banded and laminated structure. 



