Page:TransRoySocCanada 16 4 159-167.djvu/6

 when one considers the shape of the carapace, its ornamentation, the size of its marginal spines, and the faint representation of the median keel behind the cervical furrow. Woodward's figures of A. grossarti, unlike Salter's, show the cervical furrow quite distinctly, and a median keel precisely like that of A. hillianus. I retain the Nova Scotian species since it has a stronger curvature fore and aft of the lateral margins of the carapace. Thus, in the Inverness specimen, the antero-lateral angle formed by the anterior and lateral margins (neglecting the acute spine) is roughly 120° as compared with 110° in A. grossarti, too great a difference to be due to pressure. A. dubius, on the contrary, is readily distinguished by the absence of marked antero-lateral spines, the arcuate frontal margin, and the even, pronounced, strength of the median keel which runs to the posterior margin.