II.—Observations on Pterygotid Eurypterids

Synopsis With the exception ofPterygotus rhenaniœJaekel, for which the new genusJœkelopterusis 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 ofErettopterus bilobus(Salter) andPterygotus anglicusAgassiz, of the Baltic speciesErettopterus 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.