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POPULAR SCIENCE REVIEW. 
New Classification of Crustacea. —Dr. A. S. Packard, jun,, lias issued a 
sketch of his new scheme of classification for the Crustacea. He remarks 
that recent researches upon the embryology of the King Crab ( Limulus ), 
have shown certain most unexpected resemblances to the mode of develop- 
ment of the Arachnida ; * but these are also met with in certain Crabs and 
Shrimps whose development is exceptional, so that the views of some natu- 
ralists, such as E. Yan Beneden and Dohrn, that the King Crab is not a true 
Crustacean but an Arachnid, or the next thing to it, cannot be adopted. 
Limulus , according to Dr. Packard, must be regarded as a generalized or 
synthetic type combining with features of its own certain resemblances to 
the Arachnida and the normal Crustacea. In its mode of respiration, its 
external gills, and its circulatory organs, it is essentially a Crustacean ; but 
it must be separated from the normal Crustacea, and form the living repre- 
sentative of a sub-class equivalent to all the other living Crustacea. The 
fossil Merostomata (Eurypterus, Pterygotus, &c.), are closely allied to Limulus , 
and Dr. Packard considers the Trilobites to be nearly related to the Mero- 
stomata. For his new sub-class he proposes the name of Palceocarida, most of 
its representatives being old fossils ; the normal Crustacea form his sub-class 
Neocarida. 
Dr. Packard gives the following table to show the mode of arrangement 
of the different orders of Crustacea under these two sub-classes : — 
Classification of the sub-classes and orders of Crustacea. 
f 
Neocarida. 
Palceocarida. 
Decapoda. 
Stomapoda. 
Tetradecapoda. 
Phyllocarida. 
Branchiopoda. 
Entomostraca. 
Cirripedia. 
Trilobita. 
Merostomata (King Crabs, &c.) 
The Palasocarida show the following characters : — Appendages of the 
cephalothorax in the form of legs rather than jaws ; no antennae ; brain on 
the same plane as the cephalothoracic ganglionic ring and supplying nerves 
to the eyes alone ; nerves to the cephalothoracic appendages sent off from an 
oesophageal ring ; nervous system ensheathed by a ventral system of arteries ; 
metamorphosis slight ; sexes distinct. 
Order I. Merostomata. — No distinct thoracic segments and appen- 
dages. ( Limulus , Eurypterus , &c.) 
Order II. Trilobita. — Numerous free thoracic segments and jointed 
appendages. (Trilobites, all extinct.) — American Naturalist, Dec. 1879.) 
* We may remark upon an interesting piece of evidence in favour of the 
relationship between the Arachnida and Limulus, furnished by Dr. J. Barrois’ 
researches on the embryology of the Spiders. Dr. Barrois denominates an 
important stage in the development of Spiders ‘ the limuloid stage/ the 
embryo at this point having a close resemblance to the King Crabs.— See 
Ann. and Mag. Nat. Hist., March 1880. 
