135 



ON OBELISCUS (PROTOBELISCUS) RIPARIUS (Pfr.). 



By GEO. C. SPENCE. 



(Read before the Society, May 14th, 1919). 



Mr. Collier recently kindly handed to me for investigation a series 

 of the above from Antioquia Prov., Colombia, which he had obtained 

 from the DaCosta Collection. From the dried remains of the animals 

 I secured a number of embryonic shells which consist of four nearly 

 flat whorls, spire conical, columella twisted and obliquely truncate. 

 Colour pale horn, with numerous distinct white spiral bands. (In 

 well-preserved adults traces of this banding — which does not extend 

 to the post-natal growth — may be observed in the form of apparently 

 incised lines). Size : height, 7 mm. ; breadth, 4*5 mm. 



1. Obeli sciis riparhis (Pfr ). 



2. Obeliscus cuneiis (Pfr.). 

 Embryonic shells, del. ad nai. G.C.S., 22/g/ig. 



The part-grown and adult shells differ and are distinguishable at a 

 glance from O. aifieus (Pfr.). As Dr. Pilsbry in the Manual, vol. xviii, 

 page 253 (apparently from his remarks not having specimens of 

 riparius before him) reduces riparuis to a variety of cunei/s, I sent 

 the shells to Mr. Tomlin, asking him to compare them with those 

 (probably Pfeiffer's types) in the Cuming Collection in the British 

 Museum. He kindly writes me that they are identical. The 

 differences in the embryos (see annexed figures) alone prove the 

 distinctness of the two shells, and suffice to re-establish riparius as 

 a species ; but as the original description was evidently made on 

 immature specimens it is as well to add that the mouth of riparius 

 is oblique, as in O. 7najor Mill, instead of vertical, as in cuneiis. 



