136 PHYLOGENY OF FUSUS AND ITS ALLIES. 



two stronger spirals occur. On some specimens the earliest whorls 

 appear somewhat more rounded than in specimen fig". 20, but the suc- 

 ceeding whorls are angular from the strong development of the two 

 central spirals. 



Where the two central spirals cross the ribs, a flattened node of 

 rather sharp character is formed, precisely as in the neanic whorls of 

 Falsifiisits scrratns, where one node occurs, or as in Fusns asper, 

 where three nodes are found. In some specimens the next spiral above 

 approaches the main spirals in distinctness, a peripheral tricarination 

 being thus produced. Above this the spirals decrease gradually in 

 size toward the suture, while intercalated spirals may or may not occur. 

 The spirals are often crowded. The shoulder is often slightly concave 

 and the subsutural band accentuates the concavity. 



Below the peripheral angulation the spirals are more uniform and 

 subequally spaced, while intercalated spirals occasionally appear. The 

 angular appearance of the periphery is lost in the last whorl by the 

 increase in strength of the other spirals. In more accelerated speci- 

 mens the rounded contour of the body whorl is accentuated by the 

 faint character of the spirals, as well as the obsolescence of the ribs. A 

 thickening of the subsutural band produces contours characteristic of R. 

 nocu. This feature is particularly marked in accelerated individuals. 



A crowding of the lines of growth often produces a rough can- 

 cellation of the spirals. 



In a specimen in the collection of the Philadelphia Academy of 

 Sciences the protoconch, though swollen, is more depressed than in 

 the other specimens seen. It resembles in this respect somewhat that 

 of Fasciolaria. Toward the end of the first volution are faint indica- 

 tions or riblets, these becoming strong and closely set on the last part 

 of the protoconch. They then become stronger and further apart and 

 finally appear to merge into the normal ribs of the shell. The two 

 plications on the columella are not well preserved, owing to the chalky 

 character of the shell. 



RHOPALITHES ANGULATUS (Lamarck). 



(Plate IX, figs. 14-17.) 

 1803. Fusus angulatus Lamarck, Ann. du Museum, T. 2, p. 385. 

 1837. Fusns angulatus Deshayes, Coq. Foss. Env. Paris, tome 2, p. 520, pi. 74, 

 figs. II, 12. 



The protoconch of this species closely resembles that of the pre- 

 ceding one, being oblicjuely erect, smooth in the early portion, but with 

 smooth riblets in the last part. In this, as in the preceding species, there 

 are only two of the protoconch riblets in the most typical specimens. 



The conch begins with whorls in which the angulation is but slightly 

 marked and which are furnished with rounded ribs and subequal 

 spirals. This quickly merges into angular whorls, in which two spirals 



