442 PROCEEDINGS OF THE ACADEMY OF [1890. 



sides are well developed, the roof in the lower part nearly flat or 

 slightly convex. 



The upper latus is pentagonal-oval, its umbo subcentral, having 

 riblets radiating to the four lower angles ; the tergal and scutal 

 margins are about equal in length. 



Rostrum very small and short, triangular, its three sides equal. 



Rostral latus narrowly cuneiform, basal and scutal margins sub- 

 parallel, converging anteriorly, of equal length. 



Infra-median latus quadrangular, about as broad as high, the 

 rostral margin a trifle longer than the carinal ; umbo on the basal: 

 margin, 



Carinal latus narrow, sickle-shaped, recurved, longitudinally 

 ribbed, the free projecting portion about half the length of the 

 plate. 



The peduncle is long, elliptical in section. Length of capitulum 

 of the largest specimens 46 mm., width (in the middle) 32 mm. 



This species belongs to the group of S. vulgare Linn., S. magnxim 

 Darwin, S. Pfeifferi Weithofer, — species with fourteen valves, the 

 carinal latus and rostral latus narrow, compressed, with outward- 

 projecting umbones ; carina strongly angularly bent near the middle^ 

 its umbo situated nearer to the middle than to its upper termination ; 

 rostrum short, inconspicuous. 



Compared with S. magnum (coralline Crag, etc.), the present 

 species has the umbo of the carina more curved inward ; roof flatter, 

 broader. The scutum is not so narrow above, nor is the upper latus 

 so elongated. The rostral latus is truncated on its inner margin, not 

 rounded as in S. magnum. '"^■■' ' 



The triangular shape of the rostrum will separate 8. Stearnsii 

 from S. vulgare; compare also the shape of the inferior latus and the 

 carinal latus, which are quite different. This is the only recent 

 species at all approaching S. Stearnsii. 



The species described by Weithofer as S. Pfeifferi has a decided 

 resemblance to the Japanese form. It differs in the more robust 

 carina, higher, more oblique inferior latus, and in the sculpture of 

 many of the valves. aS. P/e?jfeH is from the miocene of Austria. It 

 is a much smaller species than S. Stearnsii, but not much reliance 

 is to be placed on this character. 



The principal works consulted on ScalpeUum are Darwin's 

 " Monograph on the fossil Lepadidte," in the publications of the 

 Pakeontological Society, 1851, and his "Monograph on the Cirri- 



