TETRACLITA RADIATA. 343 



fissure-like hollow. The scutum, in some distorted specimens from a 

 ship's bottom, was narrow in proportion to its ordinary breadth. 



Terga. — These are large. Externally, there is a broad, longitudinal 

 depression, bounded on each side by a ridge. The carinal half is 

 feebly striated longitudinally. A large upper portion (fig. 4 b) pro- 

 jects freely, and stands, when the two valves are articulated together, 

 above the apex of the scutum, but does not form a beak as in T. 

 porosa. Internally, the tergal margin is widely inflected ; the arti- 

 cular furrow is very deep, but the articular ridge is not prominent. The 

 spur is not very broad ; it is separated from the basi-scutal angle by a 

 small space of basal margin, which forms a straight line with the basal 

 margin on the opposite side of the spur. The end of the spur is trun- 

 cated, and is parallel to the basal margin. 



Structure of the Shell and Radii. — The walls are thick : the parietal 

 tubes are rather large and regular ; they become solidly filled up in their 

 upper parts. The sutural edges of the radii are formed by unusually 

 narrow, sinuous ridges, sending off delicate denticuli on each side : the 

 interspaces between these ridges are solidly filled up. The crenated 

 edges of the alse are rather thick. Neither the mouth nor the cirri 

 offer any noticeable character ; but I may observe, that, in the mandi- 

 bles, the third and fourth teeth are close together ; and that, in the 

 three posterior cirri, the tufts of small spines between the main pairs 

 are small. 



Affinities. — This species is very distinct from the others, with the 

 exception of the following T. radiata, to which it is in several respects 

 allied. The under side of the scutum, with its great articular ridge, 

 and the cylindrical tube formed by the union of the latter with the short 

 adductor ridge, affords the most noticeable character. 



8. Tetraclita radiata. PL 11, fig. 5# — 5 d. 



Conia radiata.* Be Blainville. Diet. Sc. Nat., 1816—1830, 



PI. 164, fig. 5, 5 a, (sine descript.) 

 — Lyonsii. G. B. Sower by. Genera of Recent and Fossil 



Shells, Plate, 1823, (sine descript.) 



* The synonymy of this species is complicated. De Blainville gives no des- 

 cription under the article Conia, published in 1818, or in the vol. published in 

 1822 ; but I believe, from the figures of the opercular valves, that I have correctly 

 identified this species with his C. radiata. Mr. Sowerby gives no description of 

 C. Li/onsii, or any figure of the opercular valves, but his drawing of the shell 

 is much better than de Blainville's, and I believe it is the same species. 

 Whether de Blainville's or Sowerby's plate appeared first I cannot ascer- 

 tain. In the second edition of Lamarck, Conia radiata of Blainville is given 

 as a synonym to Balanus radiatus of that work ; but this is quite erro- 

 neous. I may add that if de Blainville's name does not apply to the present 

 species, it must to T. ccerulescens, and as the latter is the older name it will be 



