COMPLETE HAIG: EASTERN PACIFIC PORCELLANIDAE 213 



in a simple spine, with small movable accessory spinules on posterior 

 margin. 



Telson of abdomen composed of either seven or five plates. 

 Contains 10 known species, which are confined to the west and east 

 American coasts. 



Remarks: All species referred to Megalobrachiuni and Porcellanop- 

 sis were examined during this study. When they were considered as a 

 series, ranging progressively from forms with rounded, shallow frontal 

 lobes and slender, smooth walking legs to those with deeply cut frontal 

 teeth and stout, tuberculate walking legs, it became apparent that there 

 is no clear-cut distinction between the two groups as characterized by 

 Chace (1942, pp. 99-101). It seems best, therefore, to combine all these 

 forms in a single genus, even though the extremes of the series are very 

 unlike in some respects. The following combination of characters is com- 

 mon to all these species and easily sets them apart from other genera: 

 strongly deflexed front ; basal segment of antennae broadly in contact 

 with anterior margin of carapace; and small, recessed basal antennular 

 segments. 



Key to the Eastern Pacific Species 



la. Telson of abdomen with 7 plates 2 



lb. Telson of abdomen with 5 plates 6 



2a. Carapace and chelipeds heavily eroded . . . erosum 

 2b. Carapace and chelipeds smooth to roughened, but never heavily 



eroded 3 



3a. Carpus with a narrow, blunt tooth on proximal third of 



anterior margin sinuimanus 



3b. Carpus unarmed, or at most with a slight projection at antero- 



proximal angle 4 



4a. Carapace and chelipeds thickly covered with coarse hairs 



poeyi 



4b. Carapace and chelipeds naked or lightly pubescent ... 5 

 5a. Carapace roughened ; front with three shallow lobes . smithi 

 5b. Carapace nearly smooth ; front with three teeth separated by 



deep rounded notches peruvianum 



6a. Carapace, chelipeds, and walking legs covered with small 



shallow pits garthi 



6b. Carapace, chelipeds, and walking legs tuberculate ... 7 

 7a. Antero- and posterolateral margins forming a distinct angle 

 behind mid-branchial level ; lateral margins entire . festai 

 7b. Lateral margins rounded, dentate . . . tuberculipes 



