30 BULLETIN 71, UNITED STATES NATIONAL MUSEUM. 



formed chamber in the adult often making up nearly one-half the 

 visible test and often at one side instead of bilaterally placed, in face 

 view about twice as long as wide, the last formed chamber making 

 up the larger part of the test, broadest at its base and thence gradually 

 tapering to the subacute periphery, very slightly lobulated; wall 

 smooth, punctate; aperture a narrow curved opening at the base of 

 the apertural face, simple. 



Length 0.40-0.55 mm. 



Distribution.— -The only North Pacific record for this species is that 

 of Brady in the Challenger Report, off the coast of Japan on the 

 Hyalonema-ground in 345 fathcms. 



Genus POLYSTOMELLA Lamarck, 1822. 



Nautilus (part) Linnaeus, Syst. Nat., ed. 12, 1767, p. 1162. 



Polystomella Lamarck (type, Polystomella crispa (Linnaeus)), Anim. sans Vert., 



vol. 7, 1822, p. 625.— H. B. Brady, Rep. Voy. Challenger, Zoology, vol. 9, 



1884, p. 731. 



Description. — Test composed of numerous chambers, arranged in a 

 regular, bilaterally symmetrical, nautiloid spire, the chambers ex- 

 tending back to the umbilical region so that only the last formed 

 chamber is visible, chambers either inflated with depressed sutures 

 bridged across at regular intervals or the sutures may be limbate and 

 the processes form a regular series of elevated ridges connecting the 

 sutures ; aperture either a simple opening at the base of the apertural 

 face of the chamber or subdivided into a series of openings. 



There is a considerable range of development seen in the various 

 species of this genus from the simple species such as P. striato- 

 punctata to the more complex P. crispa. In the higher species there 

 is a supplemental skeleton to the test which is provided with a rather 

 complex system of internal canals. Of these there are two spiral 

 canals, one at either side of the test comiecting with the meridional 

 canals which lie in the septal depressions between the chambers and 

 connect with the exterior by short tubes opening upon the septal 

 lines. These are best seen in P. arctica and P. sibirica, the latter of 

 which is here figured. Where the umbilical portion is filled with a 

 secondary shell material as in P. craticulata this portion is filled with 

 straight canals leading to the interior. The best figures of the 

 internal structure are those given by Carpenter. 



There is an interesting development in the species of this genus 

 and corresponding distribution. The arctic species are decidedly 

 different in many ways from the species which are so characteristic 

 of tropical coral reefs. 



