ARTHROPODA — CRUSTACEA. 



95 



pedes differing but little from advanced modern types are Gallery 

 already found in the Silurian ; these are Pollicipes and VIII. 

 Scalpelhtm. More common during that Epoch was Turri- Table-case 

 Upas, in which the body was covered with from four to six 

 columns of overlapping scales. A still older form, Lcpido- 

 coleus, had but two columns of scales. ISTot very unlike these 

 is Lorimda (Fig. 46, 6'), found in Cretaceous rocks, which 

 furnish many other genera. Most of the exhibited series, 

 however, is from the Pliocene Crags of East Anglia. 



The rest of the fossil Crustacea belong to the Sub-Class 

 MALACOSTRACA (soft shells), an old name originally 

 intended to distinguish these shell-fish " from those with 

 hard calcareous shells. There are nineteen body-segments, 

 of which eight form the thorax, and six, rarely seven, form 

 the abdomen. Most of the larger and better known modern 

 Crustacea fall within this Sub-Class. Into the unsettled 

 question of their classification we shall not here enter, but 

 merely allude to those Orders or other groups that are 

 represented by fossils. Eirst comes the group Phyllocarida, Table-case 

 in which are doubtfully but conveniently placed a numbei- -^^qq^^q 

 of Palaeozoic Crustacea, which may or may not be related 133. 

 to the recent Nehcdia. These have over the head and thorax 

 a large shield, which may be folded as in the Phyllopoda, 

 and may bear a narrow beak-like plate loosely joined to 

 it in front. The abdomen consists of ring-like segments 

 (seven in modern forms), and the telson has side-spines. In 

 Hymenocaris, from the Cambrian rocks of Wales, the shield 

 is in one piece. In Caryocaris from the same rocks it is 

 bivalve, as also in the Ordovician and Silurian Ceratiocaris, 

 which was sometimes two feet long, and in the Devonian 

 genera, Uchinocaris from JSTorth America and Aristozoe from 

 Bohemia. In Bhinocains, from the Devonian of N^ew York, 

 a third plate arose in the middle of the back between the 

 two valves. Disdnocaris and allied forms, ranging from 

 Ordovician to Trias, had an almost circular divided shield, 

 much like the brachiopod shell Discina, while Aptychopsis 

 and others have been confused with the similarly shaped 

 opercula of ammonites (compare Eig. 83). 



There have long been known from Carboniferous and 

 Permian rocks some genera differing greatly from their 

 contemporaries and placed in a division Syncarida. These 

 are now considered to resemble and to be related to a 

 remarkable Crustacean called Anaspides, which lives in 

 fresh-water pools near the top of Mt. Wellington, Tasmania. 



