644 
CLASS X. 
These animals, on a first impression, seem to have some conformity with 
the genus Limulus, although they are much smaller. They differ however 
from these greatly, as well in their oral organs, which are formed on the 
type of insects (compare Savieny Mém. sur les Ani. s. v. I. pp. 63, 64, 
Pl. vir.) as in internal structure. They undergo, as already stated in 
p- 613, a metamorphosis resembling that of Branchipus. They are found 
in fresh water, canals, fish-ponds, and pools formed by abundant rain. 
Compare G. C. Scumrrer Der Krebsartige kiefenfuss, mit 7 twlum. 
Kupfertafeln. Regensburg 1756. 4to, and HK. G. Zappacu, De A podis can- 
eriformis Anatome et Historia evolutionis, acced. tabule 4 lithogr. Bonne, 
1841, 4to. 
Sp. Apus cancriformis Latr., SoHEFFER Monogr. cit., Elem. entom. Tab. 29, 
figs. I. .; F. H. Loscucr Naturforscher, Tom. xtx. 1783, Tab. 11. ; 
GusRIN Iconogr., Crust. Pl. 34, fig. 2. 
Another smaller species has an elongate oval plate between the two 
filaments of the tail, and forms the genus Lepidwrus LEaAcH; it is the 
Apus productus LAtTR., Monoculus apus L., DESMAR. Crust. Pl. 52, fig. 2, 
GUERIN, Il. fig. 3. 
Appendix to the PHyLLopopa. 
Trilobites or Paleades. 
Fossil crustaceans. Shield cephalic, rounded anteriorly, mostly 
supplied with two lateral eyes oval or reniform, often extending 
posteriorly on each side into a horned poimt. Segments of thorax 
and 
two 
abdomen transverse, different in number, mostly divided by 
longitudinal furrows into three convex lobes. The posterior 
part of abdomen often undivided (pygidium). Body of some con- 
tractile into a ball. 
Very different opinions were entertained formerly respecting the 
Trilobites. Because the transverse segments in these fossil indi- 
viduals offered some resemblance to Chiton, LATREILLE was really of 
opinion that they ought to be placed in the neighbourhood of this 
genus. Mém. du Muséum, vu. pp. 22—32, Regne Ani. 2e édit. Iv. 
pp. 202, 203, whilst he had previously considered them to be a 
transitional form between the crustacea and the myriapoda, between 
Limulus and Glomeris (Rk. Ani. léere édit. 11. pp. 150, 151). That 
these remains belong to the type of the articulates was already 
apparent to Linnxus, who collected the few petrifactions of this 
division known to him under the name of Hntomolithus paradoxus. 
WAHLENBERG in 1818 (Act. Societ. Reg. Scient. Ups. Vol. vut. p. 1), 
in a memoir in which new species were also described, illustrated 
