166 BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



bara, California, and Northern Japan. 1 British Pliocene; Pleisto- 

 cene of Norway, Canada, Maine, and Alaska. 

 Darwin's description is as follows : 



General appearance. White, usually of a dirty tint, from the yellowish or 

 brownish persistent epidermis ; conical, generally with the parietes rugged 

 and irregularly folded longitudinally, but sometimes much depressed and 

 extremely smooth ; often cylindrical and very rugged ; occasionally club shaped, 

 the upper part being much wider than the lower ; specimens in this latter 

 condition sometimes have extremely narrow parietes, like mere ribs, and wide 

 radii. The orifice in the cylindrical varieties is often most deeply toothed. 

 The radii are generally narrow, and have jagged, oblique summits, but not in- 

 frequently they are so narrow as to form mere linear border,s, to the compart- 

 ments. The orifice is rhomboidal, passing into oval, either very deeply or very 

 slightly toothed. 



Scuta : The lines of growth are but little prominent ; the surface is generally 

 covered by disintegrating membrane. The upper ends are usually a little re- 

 flexed, so that the tips project freely as small flattened points. Internally the 

 articular ridge is highly prominent and somewhat reflexed ; there is no ad- 

 ductor ridge, but a very distinct impression for the adductor muscle ; the de- 

 pression for the lateral depressor muscle is small but variable. The terga are 

 rather small, the spur is short and placed at rather less than its own width 

 from the basiscutal angle, the basal margin slopes a little toward the spur of 

 which the lower end is rounded or bluntly pointed in a variable degree. There 

 is no longitudinal furrow, hardly even a depression. Internally the articular 

 ridge is very prominent in the upper part; the crests for the tergal depressors 

 are well developed but variable. 



Compartments. The internal carinal margin of each compartment from the 

 sheath to the basis, generally, but not invariably, projects a little inward be- 

 yond the general internal surface of the shell in a manner not common with 

 the other species of the genus; the basal edge of this projecting margin rests 

 on the calcareous basis and is crenated like the basal edges of the longitudinal 

 parietal septa. The whole internal surface of the shell is ribbed, but the ribs 

 are not very prominent. The parietal tubes are large and are crossed in the 

 upper part and often low down by transverse thin septa ; the longitudinal 

 parietal septa are only slightly denticulated at their bases ; occasionally they 

 divide at the basis close to the outer lamina of the parietes, making some short 

 outer subordinate pores. In the circular furrow beneath the lower edge of 

 the sheath there are sometimes little ridges dividing it into small cells; some- 

 times, however, this furrow is filled up by irregular knobs of calcareous matter. 

 The radii are always rather narrow, and often they form mere linear ribbons 

 of nearly uniform width along the edges of the compartments. Their summits 

 or edges are always more or less irregular and jagged, they form an angle 

 with the horizon of generally above 40. Their septa are fine, and barely or 



1 1 do not know the southern limit of D. crenatus in the eastern Atlantic. Darwin gives 

 the localities Mediterranean; Algoa Bay, South Africa; also Jamaica. Gruvel states that 

 specimens ia the Paris Museum are labeled lie King (an island in Bass Strait) and Perou 

 (Nouv. Arch, du Mus. (4), vol. 5, p. l'!9) ; and he has also recorded it from Wasin, British 

 East Africa (Bull. Soc. Zool. Franco, vol. 32, p. 164 K I hesitate to accept these exten- 

 sions of the range of crenatus into and past the Tropics until confirmed by fresh material. 

 There seems a possibility that ballast or ship-carried specimens have been picked up, or 

 there may have been a mixture of material in some of the old museum specimens. 



For the details of the range of B. crenatus in European and Arctic Seas, Weltner's Ver- 

 zeichnis and his article on cirripedes in Fauna Arctioa (vol. 1, p. 30".) may be consulted. 



