1(54 THE VOYAGE OF H.M.S. CHALLENGER. 



in so near a relation to one another as Darwin suggests, I am inclined to doubt; never- 

 theless it is true that we do not know a single fossil representative of this genus. 



What the Challenger collected as representatives of this genus is of no consequence. 

 I have, however, been obliged to describe one of the two species which the collection 

 contained as new to science. According to Darwin this genus comprises eight species ; 

 two new species were proposed by Frey and Leuckart for two forms which they considered 

 as different from Chthamalus stellatus, and which were found at Heligoland. I think, 

 however, they are only varieties of the true Chthamalus stellatus as described by 

 Darwin. 



The species of this genus may be determined with the aid of the following table : — 



Chthamalus. 



I. Scutum aud tergum completely calcified together, . . . Chthamalus intertextus, Darwin. 



II. Scutum and tergum not calcified together. 



i. Tergum with a deep narrow pit for the depressor muscle, . Chthamalus scabrosus, Darwin. 



11. Tergum without a deep pit for the depressor muscle. 



(a) Scutum with two or three furrows extending down to the 



middle of the valve, ..... Chthamalus hembeli, Conrad, sp. 



(b) Scutum without furrows. 



a Tergum with the carinal margin protuberant. 



(i.) Sutures of the walls formed by interlocking 



teeth. Tergum not elongate, . . Chthamalus dentatus, Krauss. 



(n.) Sutures of the Avails not formed by interlock- 

 ing teeth. Tergum elongate, . . Chthamalus challenger!, n. sp. 

 /? Tergum with the carinal margin not protuberant. 



(i.) Eadii with the sutural edges quite smooth, . Chthamalus antennatus, Darwin, 

 (n.) Radii with the sutural edges crenated. 



1. Terga triangular, equilateral ; orifice of the 



shell much elongated, . . . Chthamalus jfews, Darwin. 



2. Terga not equilateral ; orifice not elongated. 



(1) Membrane lining the sheath, and the 



opercular valves fimbriated, . Chthamalus cirratus, Darwin. 



(2) Membrane lining the sheath, and the 



opercular valves not fimbriated, . Chthamalus stellatus, Poli, sp. 



Chthamalus dentatus, Krauss. 



Chthamalus dentatus, Krauss, Die siidafrikanischen Mollusken, 1848. 

 C hthamalus dentatus, Darwin, Balanidae, loe. eit., p. 1G3. 



This species has the shell white or brownish, sutures between the valves formed by 

 interlocking teeth ; the tergum has a protuberant carinal margin. I refer to it some very 

 small specimens of Chthamalus, which are imbedded in the corroded surface of the large 

 specimens of Balanus tintinnabulum, taken at St. Vincent Harbour, Cape Verde Islands. 



