SUBCLASS II 



EUCRUSTACEA— CIERIPEDIA 



74: 



Pyrgoma Leach {Creusia Blainv.). Shell formed of a single piece. Base cui3- 

 shaped or sub- cylindrical ; epizoic on Corals. Lower Devonian (?). Tertiary and 

 Recent. 



Palaeocreusia Clarke (Fig. 1450). Affinities doubtful. Shell in one jiiece, with 

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



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







(?** 

 'PA 



Fio. 1449. 

 Balanus pictus Miinst. Miocene ; Dischingen, Wiirtemberg. 



Pio. 1450. 



Palaeocreusia devoniea Clarke. 

 Embedded in Farositc>:. Middle De- 

 vonian (Onondaga limestone) ; Le 

 Roy, New York. 



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

 membranous ; epizoic on whales. Pliocene to Recent. 



Ghthamalus 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. 



Eucmstacea having, in Recent forms, typically fourteen (^rarely fifteen) body- 

 somites besides 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. 



