suBCLASs II EUCRUSTACEA— CIRRIPEDIA 747 



Pyrgoma Leacli (Creusia Blainv.). Shell formed of a single piece. Base cup- 

 sliaped or sub-cylindrical ; epizoic on Corals. Lower Devoniaii (?). Tertiary and 

 Recent. 



Palaeocreusia Clarke (Fig. 1450). Affinities doubtful. Sliell in one piece, with 

 a deep cylindrical base ; epizoic on corals. Lower Devonian. 



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



Fio. 1450. 



Palaeocreusia devonica Clarke. 

 j^ j^j,j Embedded in Favosites. Middle De- 



vonian (Onondaga limestone) ; Le 

 Baianus jyictus Münst. Miocene ; Dischingen, Würtemberg. Koy, New York. 



the interior space into Chambers which open at the lower side of the shell. Base 

 niembranous ; epizoic on whales. Pliocene to Recent, 



Ghthamahis Ranz. (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. 



Superorder 5. MALACOSTRACA Latreille. 



Eucrustacea having, in Recent forms, typically fourteen {rarely fifteen) hody- 

 somites hesides the telson. All the somites {except the fifteenth) bear appendages 

 which are differentiated into two groups, a thoracic of eight and an abdominal of 

 six pairs. 



The Classification of the Malacostraca has undergone considerable modifi- 

 cations at the hands of zoologists within recent years, and further research is 

 necessary before some of the fossil forms can be assigned to their proper 

 places in the newer arrangements. 



The basis of the new Classification is the recognition of the fact that what 

 has been called the " caridoid facies " is a common inheritance from the 

 primitive stock of the Malacostraca (possibly excepting the Phyllocarida), 

 and does not imply close affinity between the various groups presenting it. 

 The Chief characters that go to make up this facies are the stalked eyes, the 

 scale-like exopodite of the antenna, the thoracic carapace, the natatory 

 exopodites of the thoracic limbs, the large and ventrally flexed abdomen, 

 and the " tail-fan " formed by the uropods and telson. The group " Schizo- 

 poda " has long served as a receptacle for primitive forms possessing these 

 characters, and its dismemberment into the three orders, Anaspidacea, 

 Mysidacea and Euphausiacea, is attended by the inconvenience that the 

 characters distinguishing these Orders are but rarely to be discovered in 

 fossils. 



