82 Dr. J. Micldehorough — 



about 18*5 centimeters (7f inches) long; in witltli 11'5 centimeters 

 (about 4-| inches). On the ventral surface a broad median groove 

 extends along the concavity of the thorax and abdomen. It begins 

 at a point beneath the articulation of the head with the thorax, or 

 in the posterior part of the area between the lobes of the hypostoma. 

 Its length is lO'S centimeters (4^ inch) — 6'5 centimeters being the 

 length of the thoracic, and four centimeters that of the abdominal 

 portion of the groove. This specimen clearly demonstrates the 

 coHCOi'% of the three principal divisions of the Asaphus, a fact which 

 Mr. Billings pointed out in 1864. The vertical distance from the 

 dorsal surface of the head to a line in the plane of the external 

 margins of the pleurse is 2-5 centimeters (about one inch). 



Directly beneath the eight somites of the thorax, ten pairs of 

 jointed limbs are distinctly seen ; the two anterior pairs of appendages 

 are situated directly under the first two thoracic segments ; but from 

 the character of these appendages, as well as the relation of parts, 

 these, while having the general appearance of organs of locomotion, 

 yet were, no doubt, maxillipedes with the basal joints articulated to 

 the body of the animal, near the point where the oral aperture 

 certainly existed, and presumably they were differentiated to perform 

 the function of mouth organs, and consequently should be considered 

 as belonging to the cephalic division. The remaining eight pairs of 

 legs are then directly referable to the eight thoracic somites. The 

 number of joints in a limb cannot be definitely given from a study of 

 these specimens ; the basal joints are not preserved at the median 

 groove. 



Following the terminology of Milne-Edwards for the several parts 

 of the limb of a crustacean, the prominently-marked portion of these 

 ambulatory limbs is undoubtedly the meropodite, which was in some 

 cases two centimeters in length and quite large, with the mei'o- 

 carpopodite articulation well pronounced, so as to leave a distinct, 

 pit-like depression in the matrix. The several joints externally to 

 that which is considered the meropodite can be distinguished by 

 careful study of the several legs and the grooves and foveas of the 

 matrix. The carpopodite was about the length of the meropodite, 

 but decidedly slender as compared with the latter. If there was 

 any positive evidence to show that these were broad, lamellar append- 

 ages, adapted to swimming, then the slender joints external to the 

 meropodite might be accounted for by supposing the edges were 

 the portions visible. The propodite was about two-thirds the length 

 of the carpopodite, and also appears to have been slender and slightly 

 curved backward ; the dactylopodites are not well preserved, yet 

 sufficiently so to permit the conclusion that they were not chelate. 

 The posterior pair of these thoracic appendages is directly beneath 

 the posterior somite of the thorax. The meropodites of the two 

 anterior pairs of appendages resemble the same joints in the 

 thoracic limbs. 



In examining the matrix, where the left limb of the anterior pair 

 is well preserved, it is seen to curve around the outer margin of the 

 left lobe of the hypostoma, and from the evidence which the surface 



