No. 402.] MWORTH-AMERICAN INVERTEBRATES. 513 
B’. Rostrum almost horizontal . . M. camptocerum (Stimpson), G 
A’. Carapace without dorsal spines except the epibranchial and posterior 
spines . - M. [ani (Latreille), M( CH)G 
Genus Ccelocerus k Milne Edwards M . C.grandis Rathbun, G 
Genus Libinia Leach. 
Key to Species. 
A. Carapace with lateral margin evenly rounded behind the rostrum. 
B. Median spines six . . : . . L. dubia Milne-Edwards, MSG 
B’. Median spines nine . ner ^ md Leach, VSG 
A’. Carapace distended at ae hepalie regions Z. spinimana Rathbun, G 
Fic. 8. — Mithrax acuticornis. 
KEY TO THE GENERA OF THE FAMILY PARTHENOPID. 
A. Carapace not laterally expanded. 
B. Carapace tuberculate. 
C. Carapace triangular, convex. Pterygostomian and subhepatic 
regions not deeply excavated to form passages to the effer- 
ent branchial apertures . Lambrus 
C'. Carapace sabriouboliigl. Ment. Pierygostomian and 
subhepatic regions excavated, this excavation forming, 
when the chelipeds are retracted, passages to the efferent 
branchial apertures . . AE NAT atylambrus 
B'. Carapace smooth . . . Solenolambrus 
A’. Carapace more or less tapssded. to "Dus a vadit i in which the ambu- 
latory legs are concealed. 
B. Carapace greatly expanded, both laterally and posteriorly 
Cryptopodia 
B'. Carapace expanded laterally, but not posteriorly . Heterocrypta 
