MOLLUSCA OF THE * CHALLENGEK ' EXPEDTTTOK. 



587 



would of course exhibit it ; but all the specimens I have seen are 

 more or less chipped. 



The nacre of the shell is a feature that connects this genus with 

 the Trochidae. The nacreous layer is evidently not thick ; and 

 when the shell is young and perfectly fresh it is altogether so 

 translucent that the nacre hardly appears as more than a pearly 

 lustre; and in all cases it has more of the beauty of the actual 

 pearl than that of the mother-of-pearl shell, but the nacreous 

 layer is unmistakably present. The exterior calcareous layer is 

 thin and very highly translucent, but still not glassy. 



List of Species. 



1. Seguenzia formosa, Jeffr. 3. S. carinata, Jeffr. 



2. S. ionica, W. 4. aS^. trispinosa, W. 



1. Sequenzia FORMOSA, Jeffr. 



St. 24. K of Culebra Island. St. Thomas, Danish W. Indies. 

 March 25, 1873. 390 fms. Several young and broken specimens. 



St. 56. Bermudas. May 29, 1873. 1075 fms. Glohigerina- 

 ooze. 4 specimens, hardly full-grown. 



Yar. LiXEATA, W. 



St. 120 ? Pernambuco. Lat. 8° 73' S., long. 34° 28' W. Sep- 

 t ember 9, 1873. 675 fms. Mud. 1 young specimen. 



St. 122? Pernambuco. Lat. 9° 10' S., long.^34° 50' W. Sep- 

 tember 10, 1873. 350 fms. Mud. 1 young specimen. 



J. Gr. Jeffreys, ' Valorous ' Expedition, Koy. Soc. Proc. No. 

 173, 1876, p. 200 :— From N. Atlantic, 1450 fms. Bay of Biscay, 

 Spain, and Portugal, 718-795 fms. Gulf of Mexico, 325 fms. 

 Fossil, Trapani, Sicily {Seguenzia). 



Shell. — Small, conoidal ; spire high ; base inflated, white, glossy, 

 with high spiral threads. Sculpture. Of spiral threads there 

 are ten on the last whorl — one small, sharp, just at the suture ; 

 two, strong and sharp, of which the lower forms the basal 

 carina; the upper, which issometimes even the more pro- 

 minent, lies a little higher than halfway between the basal and 

 the sutural spiral : on the base there are seven, very equal in 

 strength and in distribution — the first lies somewhat remote 

 from the basal carina, and is separated from it by a broad 

 shallow furrow ; the last lies pretty close to the pillar and 

 twines round it. On the upper whorls only the sutural and 

 supracarinal spirals are seen. There are microscopic spirals 

 on all the surface. Longitudinals — there are many hair-like, 



43* 



