226 U.S. NATIONAL MUSEUM BULLETIN 29 2 



Gastric region (Gst). The principal mesial area on the carapace lying anterior 

 to the cervical groove and bounded posteriorly by the cardiac region, laterally 

 by the branchial and hepatic regions, and anteriorly by the frontal and 

 orbital regions; in tlie true crabs, it comprises the unpaired mesogastric 

 and metagastric regions, the urogastric lobe, the paired protogastric regions, 

 and the epigastric lobes. 



Hepatic region (Hep). Paired anterolateral areas on the carapace bounded pos- 

 teriorly by the brancliial region, mesially by the gastric region, and anteriorly 

 by the orbital or (in the shrimps) antennal region. 



Hepatic spine (hepSp). A lateral spine situated near the anterior margin of the 

 hepatic region on the carapace of certain shrimps; it probably represents 

 the branchiostegal spine displaced posteriorly from the anterior margin of 

 the carapace. 



Intestinal region (Int). The most posterior of the mesial areas on the carapace 

 of crabs, bounded anteriorly by the cardiac region and laterally by the 

 branchial regions. 



Ischium, pi. -chia (Isc). The third segment from the proximal end of a typically 

 7-segmented appendage. 



Lateral wall. The subvertical portion of the carapace of crablike decapods ex- 

 tending ventrally from the lateral margin. 



Lentic. Pertaining to standing water, as in lakes, ponds, and swamps. 



Lotic. Pertaining to running water, as in rivers and smaller streams. 



Mandible (Md). One of the heavily calcified jaws lying anterior to (beneath, 

 in ventral view) the other mouth parts but visible in certain crabs. 



Maxilliped (Mxpd). One of a pair of three sets of cephalothoracic appendages 

 arising posterior to the primary mouth parts. The most prominent set, the 

 third or outer maxillipeds, are, in the shrimps, slender elongate appendages 

 resembling the pereiopods and, in the crabs, broadened and flattened struc- 

 tures that close to form a more or less complete operculum over the other 

 mouth parts. 



Merus, pi. meri (Mer). The fourth segment from the proximal end of a typically 

 7-segmented appendage. 



Mesobranchial region (msBr). The intermediate portion of the branchial region 

 on the carapace of crabs. 



Mesogastric region (msGst). The central portion of the gastric region on the 

 carapace of crabs. 



Metabranchial region (mtBr). The posterior portion of the branchial region on 

 the carapace of crabs. 



Metagastric region (mtGst). The posteromesial portion of the gastric region on 

 the carapace of crabs. 



Orbit (Orb). The eye socket or excavation in the anterior margin of the carapace 

 in which the eye is lodged. 



Orbital region (Orbl). The paired areas on the carapace adjacent to the orbits. 



Palm (Plm). The portion of a chela proximal to the fingers. 



Palp (Pip). The two or three distal segments of the third maxilliped of crabs 

 distal to the merus. 



Pereiopod (Prpd). One of the five posterior paired appendages or legs attached 

 to the cephalothorax. 



Petasma (Ptsm). A complex genital structure attached to the mesial margins of 

 the protopodites of the first pair of pleopods in male penaeidean shrimps. 



