EAST AMERICAN SGAPHOPOD MOLLUSKS. 45 



As appears in the description, and as might be expected in a shallow- 

 water species of wide distribution, there is here a considerable range 

 of variation, except only in the degree of curvature and in the general 

 shape of the shell. These variations appear in the amount of prom- 

 inence of the intercostal transverse sculpture. In the majority of 

 specimens observed the longitudinal ribs are flat on top and are of 

 about the same width as the spaces between them. Another form, 

 which is mostly Cuban, has sharper, narrower ribs and shows but little 

 intercalation. Another, which is also chiefly Cuban, has the number 

 of its ribs increased by a double system of intercalation, and all the 

 ribs so greatly widened and flattened that the spaces between are 

 reduced to mere threads. This is the usual form that is found in 

 Habana and Bahia Honda Harbors, though it is not confined to those 

 two localities. In some forms the nine primary ribs are not clearly 

 observable, owing to their almost immediate increase by intercalated 

 secondaries even upon the slender tips, and as the tips are seldom 

 preserved the shell appears to possess more than nine original ribs. 

 The varying degree of intercalation, therefore, makes the actual num- 

 ber of ribs exceedingly inconstant. The curious maculation of the ribs, 

 however, as already stated, is a constant and most striking feature. 



The protean character of this species at first led me to divide it into 

 several subspecies, but my divisions always became hopelessly con- 

 fused by intermediates, and furthermore refused to conform with any 

 distributional principles. I abandoned all attempts to subdivide the 

 variable assemblage here included under Orbigny's meager descrip- 

 tion. This is the result of a long, patient study of the abundant 

 material at my disposal. 



Extreme forms of this species closely resemble the stouter forms of 

 Dentaliu7n ceratum, but may be distinguished by their greater curva- 

 ture, their greater diameter and tliickness in the apical portion, their 

 less smooth and glossy surface in the anterior portion, and by the per- 

 sistent gray color spots on the ribs. Worn fragments of the middle 

 portion of the shell are often quite indistinguishable from D. ceratum. 



Topotypes, Cat. No. 2500S9, U.S.N.M., are in the museum collec- 

 tion from St. Thomas. Lots from the Florida Keys, Tortugas 

 (Eolis), northwest coast of Cuba, from Esperanza and Cape San Anto- 

 nio (Barrera Expedition), Habana, Bahia Honda, Cardinas (Barrera 

 Expedition), Bimini Islands (Eolis), Samana Ba}^, Barbados, are all 

 littoral. 



This is the most common shallow-water West Indian Dentalium, 

 ranging from Barbados throughout the Lesser Antilles, Santo Do- 

 mingo, Cuba, Florida, Bahamas, All the deep-water records for this 

 species quoted by authors should be regarded as erroneous and as 

 probably referring to other species confused with D. antiUarum. 



