ON A NEW LABKADOREAX SPECIES OF ONCHIDIOPSIS 

 A GENUS OF MOLLUSKS NEW TO EASTERN NORTH 

 AMERICA; WITH REMARKS ON ITS RELATIONSHIPS. 



By Francis N. Balch, 



Of Boston, Massachusetts. 



During the summer of 1908 Mr. Owen Bryant, cruising on the Labra- 

 dor coast, made opportunity for some dredgings in moderate depths. 

 The resulting mollusks, with the exception of the Nudibranchs, were 

 placed in the hands of Mr. C. W. Johnson, curator of the Boston 

 Society of Natural History. The small collection of Nudibranchs 

 was intrusted to me. In it was included an apparently naked mol- 

 lusk, which Mr. Bryant took for a dorid form, hut which is in fact 

 a fine new species of the internal-shelled genus OncJiidiopsis belong- 

 ing to the family Lamellariidse. Mr. Bryant's mistake was far from 

 unnatural, and it is possibly owing to similar errors on the part of 

 other collectors that we owe almost all our knowledge of the group 

 to specialists on the Opisthobranchiata (especially the Nudibranchs), 

 as will appear from the literature cited at the end of this paper. 



The specimen is a fine adult, well preserved in formol, and is of 

 interest from several points of view — first, from the point of view 

 of geographical distribution, the genus being previously unknown 

 from eastern America, though present in Greenland and Alaska; sec- 

 ond, from the point of view of systematic morphology, the genus 

 being probably the last term of an extraordinary aberrant series 

 and containing few, perhaps only one, hitherto known species; third, 

 from the point of view of teratology, since the specimen has a bifid 

 left tentacle the abnormal member of which bears what appears exter- 

 nally to be an extra ey'e resembling the normal, out proves on section- 

 ing to be a group of four eyes apparently proliferating one from the 

 other, in various stages, making a case quite unique so far as the 

 records show. 



The present paper contains a description of the specimen, with a 

 brief discussion from the first and second points of view. The tera- 

 tological aspect, was presented in a separate paper read before the 

 American Society of Zoologists (Eastern Branch i during convocation 

 week in Boston, December, 1909, and which, it is expected, will be 

 published in the American Naturalist. 



Out of a desire not to mutilate the single specimen more than 

 necessary, ex a mi mi lion has been confined to external points and to the 



Proceedings U. S. National Museum. Vol. 38— No. 1761. 



469 



