652 



ABTHKOPODA 



SUB-KINGDOM VII 



six pieces. Opercular p]ates sub-triangular ; base membranous or calcareous. Eocene 

 to Recent. 



Protobalanus, Whitf. Composed of twelve plates, of which the carina is the 



largest ; rostrum small, lateralia 

 in five pairs, fused only near the 

 base. Middle Devonian. 



Acasta, Leach. Shell com- 

 posed of six solid pieces. Base 

 calcareous, cup -shaped; attached 

 to sponges and Alcyonarians. 

 Pliocene and Recent. 



Pyrgoma, Leach (Creusia, 

 Blainv.). Shell formed of a single 

 piece. Base cup - shaped or sub- 

 cylindrical ; attached to corals. 

 Lower Devonian. Tertiary and 

 Recent. 



Palaeocreusia, Clarke (Fig. 

 1368). Shell in one piece, with 

 a deep cylindrical base ; attached 



FIG. 1366. 



Balanus concamis, Bronn. Crag ; Sutton, England. A, Shell. 

 B r Tergum. C, Scutum. 1/1 ( af ter Darwin). 



to corals. Lower Devonian. 

 Coronula, Lam. Composed of six lateralia, with thin, deeply folded walls dividing 



FIG. 1367. 

 Balanus pictus, Miinst. Miocene ; Dischingen, Wiirtemberg. 



FIG. 1368. 



Palaeocreusia devonica, Clarke. 

 Embedded in Favosites. Corniferous ; 

 Le Roy, New York. 



Base 



the interior space into chambers which open at the lower side of the shell, 

 membranous ; parasitic on whales. Pliocene to Recent. 



Chthamalus, Rauz (Euraphia, Conrad). Shell depressed, composed of six pieces. 

 Base membranous. Cretaceous, Miocene, and Recent. 



Pachylasma, Darwin. Shell in the young with eight pieces, which afterwards become 

 six, or by coalescence of the lateralia are apparently reduced to four. Base calcareous. 

 Pliocene to Recent. 



Super-Order 5. MALACOSTRACA. Latreffle. 



Eucrustacea having, in recent forms, a constant number (twenty or twenty-one) of 

 segments. Cephalothorax composed of thirteen segments, and bearing the same number 

 of appendages. Abdomen distinct, heptamerous (except in the Phyllocarida), the 

 terminal joint being known as the telson. 



Under this head are included the orders Phyllocarida, Stomatopoda, Decapoda, 

 and Arthrostraca, all of which have fossil representatives. 



