a1 Department of Geology, Royal Scottish Museum.
With the exception of Pterygotus rhenaniœ Jaekel, for which the new genus Jœkelopterus is proposed, the published accounts of the median abdominal appendages of the Pterygotidæ are inadequate. An examination of the British material was undertaken with a view to improving our knowledge of the opercular anatomy of the family. An account is given of the genital appendages associated with both sexes of Erettopterus bilobus (Salter) and Pterygotus anglicus Agassiz, of the Baltic species Erettopterus osiliensis (Schmidt) and of British forms in which only one type of appendage is known. Attention has been given also to the cheliceræ of the British type species because of the importance which has been attached to this character in classification. The significance of the chelate and genital appendages in the classification and biology of the Pterygotidæ is discussed.
(Received November 25 1963)
(Revised January 16 1964)
* This paper was assisted in publication by a grant from the Carnegie Trust for the Universities of Scotland.