220 ASTRALIUM. 



Gemis ASTRALIUM Link, 1807. 



Shell trochiform, generally more or less flattened above or below; 

 imperforate or umbilicate ; young speciynens ahvays carincded and 

 spinose at the periphery ; operculnm oval or oblong, with (except in 

 JBolma) submarginal or terminal multispiral nucleus; the last 

 whorl forming far the greater portion of the operculum, usually 

 with one or several ribs exteriorly, following the course of the spiral 

 and most elevated at the distal extremity. 



The synonyms are Calear (Montf.) Fischer and other authors, 

 Imperator (Montf) Auct., Trochus, in part, of all earlier authors, 

 and Tarho, in part, Sowerby Jr. and others. 



Authors have been consideral)ly at variance in regard to both 

 the limits and the proper designation of this genus. I have exam- 

 ined the history of every name proposed for species of the group, 

 either as generic or subgeneric, and find that none prior in date to 

 that of Link (1807) are entitled to any standing in nomenclature, 



I am indebted to Dr. W. H. Dall for a copy of Link's description 

 of Astralium. It was defined in the Beschreihung der Naturlien- 

 Sammlnng der Universitdt zii Rostock, von D. H. F. Link, Professor, 

 etc., p. 134-135, May 17, 1807 ; the genus is briefly described by 

 Link and ^4. deplanoium given as the first species, with a reference 

 to figures in Chemnitz, which fix the identity of deplanatmn with 

 Lamarck's A. costulatum, a species of the West Indian group. 



Those species having a turbinate form, convex base and rounded 

 periphery, such as ^4. rugosum, A. cwlatinn, A. tuber, have been 

 frequently adduced by authors as supplying the connecting links 

 between Turbo and Astralium ; but such resemblance as they have 

 to Turbo is to be attributed not to any real relationship, but to a 

 secondary modification which they have undergone from the stellate 

 forms of Astralium. That this is the case is shown by the young of 

 the turbinate species, Avhich we find to be flattened, acutely carinated 

 and spinose, precisely as in typical Astralium. As a rule, the young 

 of species of this genus are depressed, carinated and spinose at the 

 periphery, the sjiines frequently being reduced in size or lost in the 

 adult ; whilst in Turbo the young are in the spinose species smoother 

 than the adult, the spines becoming always more prominent with age. 



The real connecting forms between these genera the student must 

 look to palaeontology to supply; for the recent species which at first 

 seem to be intermediate in characters are undoubtedly descending 

 from stellate types of Astralium. 



