240 BULLETIN OF THE 



tracery, usually "white inside, but occasionally very dark brown, this character 

 being apparently local; the concentric wrinkles are close but less strong, a 

 little wear makes them seem absent, and the shell smooth ribbed ; the same 

 dilFerences exist as to truncation ; this character is probably sexual. 



The variety carinatv^ has the same number of ribs as the typical form, but 

 they are carrnated, and the interspaces toward the margin, owing to impressed 

 radiating lines, seem to have several small threads in them between the ribs ; 

 the concentric wrinkles are more distant, and take a lamellate aspect, forming, 

 with the ribs, a reticulation which seems very characteristic ; the shell is a 

 little more globose than the ordinary form, but not much ; otherwise it seems 

 precisely the same, and all the gradations, from flat wrinkled ribs to keeled 

 and reticulated ones, may be seen in the series before me. A single one taken 

 by itself would certainly appear distinct from the ordinary form, and this gives 

 us a hint of what we may expect when large numbers of specimens come to be 

 studied scientifically and with due regard to their geographical distribution. 



Genus ARCA Linn^. 



Area pectvmcTiloides Scacchi, var. orbiculata. 



Area pectunculoides Scacchi, var. orbiculata, Dall, Bull. M. C. Z., IX. p. 121. 



Plate VIII. Fig. 5. 



Habitat of the variety : Gulf of Mexico, Station 33, 1568 fms. (one valve). 



Typical form : Sigsbee, oflF Havana, in 480 fms.; Station 16, near Havana, 

 in 292 fms., living, bottom temperature, 66° ; Station 176, near Dominica, in 

 391 fms.; Station 211, near Martinique, in 357 fms.; and Station 230, off St. 

 Vincent, living, in 464 fms., bottom temperature 41°.5 F. 



Examuiation of a large number of specimens in the Jefireys collection has 

 convinced me that the single valve described as variety orbiculata is merely 

 an extreme variety of the typical pectunculoides, and not distinct, as I suspected 

 then. It is, however, certain that all the American specimens are shorter and 

 rounder than those from farther east in the Atlantic sea-bed and the Norwegian 

 and arctic seas. 



Area grenophia Eisso may be this species, but it was not figured, and the 

 description is quite insuflicient. Area pectunculoides, var. crenulata Verrill, 

 appears to have the form of var. orbiculata, the teeth of the Gulf specimens 

 above mentioned, the marginal crenulations of glomerula, and the sculpture 

 of the type of pectunculoides. I have only seen one right valve of crenuloM, 

 but both valves seem to be sculptured alike. 



By a slip of the pen, in treating of Area glacialis Gray, Prof. Verrill (Trans. 

 Conn. Acad., V. 576, 1882) represents me as recording A. glacialis from the Gulf 

 of Mexico. This is an error ; as, in mentioning it in the Blake Preliminary 



