NOMENCLATURE OF THE SHELL OF A SESSILE CIRRIPEDE. 



ARCHETYPE SHELL. Fig. 1. 



Orifice of shell, surrounded by the sheath. Sheath formed by the alee (a — a) and by portions of the 

 upper and inner surfaces of the parietes (p — p). 



p p Parietes 



Basis 



3 t 



n. b. In Balanus, and all known fossil genera, the Rostrum and Rostro-lateral compartments are confluent, 

 and hence the Rostrum has the structure of Fig. 2. 



Fig. 2. 



COMPARTMENTS. 

 Fig. 3. 



Fig. 4. 



Occludent Margin 



Cavity for Adductor 

 Muscle 

 Adductor Ridge 



Fig. 2. Compartment with two radii, serving, in fossil specimens, always as a Rostrum. 

 Fig. 3 serves as a Lateral and Carino-lateral Compartment. Fig. 4 serves as a Carina. 



OPERCULAR VALVES. 

 Fig. 5. Scutum (internal view). Fig. 6. Tergum (internal view) 



^Tergal Margin Apex 



i-L Articular Ridge 



■ Articular Furrow 



Cavity for the Lat. 

 Depressor Muscle. 



Articular Ridge _..J... 

 Articular Furrow ..._L 

 Scutal Margin J 



Carinax Margin 



Crests for Depressor 



Muscle. 

 Basal Margin 



Spur. 



Fig. 7. Tergum (external view). 

 Beaked Apex 



-Carinal Margin 



Scutal Margin 



Spur 



Basal Margin 



