10 CALIFORNIA ACADEMY OF SCIENCES. 



The typical Macrouran carapace is elongated, and the 

 anterior end is produced into a rostrum. The anterior 

 region of the carapace is often furnished with teeth or 

 spines which occur in the following positions: the supra- 

 orbital spine, or spines, above the orbit; the suborbital 

 spine on the anterior margin of the carapace below the 

 orbit; the antennal spine below the last and behind 

 the base of the antenna; the hepatic spine on the he- 

 patic region. Any or all of these spines may be present 

 or absent. There is generally visible a groove, known 

 as the cervical groove, which extends downwards and 

 forwards from the dorsal surface of the carapace, mark- 

 ing the line of union of the head and thorax. The 

 dorsal surface in front of this groove is termed the 

 gastric region, the hepatic regions lying at the sides; 

 immediately behind the gastric region is the cardiac, 

 while the intestinal region lies behind the latter at the 

 posterior end of the carapace; the sides of the carapace 

 behind the cervical groove are known as the branchial 

 regions, since they form a covering for the branchiae, 

 or gills. 



In the Brachyura the carapace is wide and generally 

 flattened, and the rostrum is small or absent. The 

 regions are generally separated from each other by sulci, 

 or grooves, and there are usually more regions marked 

 out than in the Macroura. The cervical groove is 

 usually visible and divides the gastric and hepatic from 

 the cardiac and branchial regions. On the sides of the 

 carapace below the lateral -margins there are (1), the 

 pterygostomian region on either side of the mouth area 

 and (2), the sub-branchial regions below the branchial 

 areas. The names of the regions which appear on the 

 dorsal surface may be obtained from fig. 2. The dis- 

 tinctness of these areas is subject to great variation in 



