NOMENCLATURE. 5 



lation of the name already used by some authors, of Keel- 

 Valve. 



The Rostrum has been so called from its relative 

 position to the carina or keel. There is often a Sub- 

 carina and a Sub-rostrum. 



The remaining valves, when present, have been called 

 Later a ; there is always one large upper one inserted 

 between the lower halves of the scuta and terga, and this 

 I have named the Upper Latus or Latera; the other 

 latera in Pollicipes are numerous, and require no special 

 names ; in Scalpellum, where there are at most only three 

 pair beneath the Upper Latera, it is convenient to speak 

 of them (vide Woodcut, I,) as the Carinal, Infra-median, 

 and Rostral Latera. 



As each valve often requires (especially amongst the 

 fossil species) a distinct description, I have found it in- 

 dispensable to give names to each margin. These have 

 mostly been taken from the name of the adjoining valvej 

 (see fig. I.) In Lepas, Pollicipes, &c, the margin of the 

 scutum adjoining the tergum and upper latus, is not divided 

 (fig. II) into two distinct lines, as it is in Scalpellum, 

 and is therefore called the Tergo-lateral margin. In 

 Scalpellum (fig. I) these two margins are separately 

 named Tergal and Lateral. The angle formed by the 

 meeting of the basal and lateral or tergo-lateral margins, 

 I call the Baso-lateral angle ; that formed by the basal 

 and occludent margins, I call, from its closeness to the 

 Rostrum, the Rostral angle. In Pollicipes the carinal 

 margin of the tergum can be divided into an upper and 

 lower carinal margin ; of this there is only a trace (fig. I) 

 in Scalpellum. 



That margin in the scuta and terga which opens and 

 shuts for the exsertion and retraction of the cirri, I have 

 called the Occludent margin. In the terga of Lepas 

 (fig. Ill) and some other genera, the occludent margin 

 is highly protuberant and arched, or even formed of two 

 distinct sides. 



Occasionally, I have referred to what I have called the 



