430 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 5 



From the fact that Finnegan (1931) records the mainland species, 

 P. rotundata (Stimpson) (1860) from the Galapagos Islands, it might 

 be expected that some of the Hancock series would prove to be of that 

 species also. However, comparison of selected pairs with the type of P. 

 gemmata (USNM No. 24830) and with the Rathbun photographed 

 specimen of rotundata (No. 4079) collected by Capt. Dow at Panama 

 conclusively shows all Hancock Galapagos Platypodias to be gemmata, 

 none having the linear mesogastric or bifid protogastric region of 

 rotundata. 



Platypodia rotundata (Stimpson) 



Atergatis rotundatus Stimpson, Ann. Lye. Nat. Hist. New York, vol. 7, 



p. 202 (74), 1860. 

 Platypodia rotundata Rathbun, Proc. U.S. Nat. Mus., vol. 38, p. 584, 

 1910; Bull. 152, U.S. Nat. Mus., p. 248, pi. 102, figs. 1-3, and 

 synonymy, 1930. Finnegan, Journ. Linn. Soc. London, Zool., vol. 

 37, no. 255, p. 633, 1931. 



Type locality. — Cape San Lucas, Lower California. 



Types. — Cotypes in MCZ. 



Range. — From La Paz, Gulf of California (Lockington), to Pta. 

 Santa Elena, Ecuador (Schmitt) ; Galapagos Islands (Crossland). 



Atlantic analogue. — P. spectabilis (Herbst). 



Diagnosis. — Carapace rotund, areolate, margin cristate. Mesogastric 

 region narrowed anteriorly, protogastric region divided into two distinct 

 lobules. 



Material examined. — None from the Galapagos Islands. The Han- 

 cock collections contain a long series of this species from Escondido Bay, 

 Gulf of California, to Santa Elena Bay, Ecuador. 



Remarks. — Since Finnegan (1931) recorded both P. gemmata and 

 P. rotundata from among Galapagos material collected by Crossland on 

 the St. George Expedition, it is presumed that she was familiar with the 

 distinguishing features of both species. However, her inclusion of P. 

 gemmata, regarded heretofore as a Galapagos endemic species, in the 

 Taboga Island, Bay of Panama, fauna, where rotundata would be ex- 

 pected, suggests that she may have placed too much emphasis upon the 

 presence or absence of hair in the depressions of the carapace, a feature 

 given as diagnostic by Rathbun (1930), and not enough upon the shape 

 of the proto- and mesogastric regions, which is the structural basis for 

 separation of the two species. 



