- IGO - 



inal area as in the typical Argina; hinge with about fifteen post- 

 erior and nine anterior teeth, the tvro aeries im interrupted; inner 

 marsTin of the valve deeply crenulated. 



Siraensions .- Length, 6.1 mm.; max. alt. 5.9 mm.; semidiara., 

 1.8 mm. ; leng''"h of hinge, 4 mm. 



Remarks .- '^he descilption of the right valve niay he incorrect 

 since the only right valves at hand are very small forms which 

 are douhtfiilly referred to this variety. It seems iir.prohahle that 

 only left valves of one species and rifht valves of another should 

 aripear and therefore these right valves are considered microtera . 

 although they display characters different from those that v/ould 

 be expected. Right valves of the section Arjrina are smaller than 

 left ones and usually have fev;er and lower ribs, but in this ease 

 the flisnarity in the number of ribs is inordinate and the ribs are 

 more sharply sculptured on the right valves, even projecting be- 

 yond the margin in the anterior and meUan regions of the shell. 

 In addition the right valves are more rounded aad have umbones 

 ^hat are only obscurely suicated. 



This form has previously been referred to as A, tolepia , a 

 name which Dall proposed for a species from Santo Domingo and Ou- 

 m^na Trhich Guppy (l) erroneously identified with the recent A, 



(1). Geol. I'ag., Decade 2, vol. 1, p. 'AZ (check list). 



