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Show 158 • MR. R. COLLETP ON ECHIDNA ACANTHION. [Feb. 3, membranous tissue. One (the left?) was the larger, and had a length of about 57 millim., a breadth of 40 millim.; its greatest thickness (at the outlet of the lacteal ducts) was 22 millim. The other was a little smaller. The "mammary areola" was visible on the belly as a flattish spot. No trace of a pouch could with certainty be distinguished (in the single mounted female specimen). In the mounted full-grown male was visible on each side of the belly (where the mammary areola is found in the female) a small vortex of hairs, apparently an indication of the rudimentary mamma of the males of other mammals. Parasites.-In two specimens I found half a dozen individuals of an Ixodes, attached between the hairs at the root of the dorsal spines or in the ear-tuft. Comparison with E. aculeata.-Whilst E. acanthion will be easilv distinguishable from E. aculeata by its external characters, the skeletons of both species are more difficult to distinguish. Yet, compared with a skeleton of E. aculeata of the same size, that of E. acanthion will be seen to be decidedly slenderer. Thus when the skeleton No. 3, with a total length of 448 millim., is laid side by side with a skeleton of E. aculeata, the total length of which is 450 millim., all the vertebrae from the head to the pelvis show themselves as perceptibly narrower and weaker ; whilst the breadth of the penultimate lumbar vertebra in E. aculeata was 20 millim., the same vertebra in E. acanthion was only 16\ millim. broad. The jjrocessus spinosi of the first dorsal vertebra did not (yet) show any trace of being notched in E. acanthion, whilst the notches were distinct in the other species. The humerus is weaker and narrower. The breadth between epiccndylus medialis and lateralis (i. e. the greatest breadth on the ulnar side) is in E. aculeata 47 millim., in E. acanthion 41 millim. only ; the breadth between trochanter medialis and lateralis (i. e. the greatest breadth on the scapular side) is 31 millim. in E. aculeata, and 27 millim. in E. acanthion. The scapula is shorter and is more straight. Its greatest length (to the articulation with humerus) in E. aculeata is 56 millim., in E. acanthion 51 millim. ; in the latter species the maryo superior is almost straight, but more bent outwards in E. aculeata. The ribs are not narrower in E. acanthion than in the other species ; but the pelvis is decidedly weaker. Whilst thus the length from the upper end of os ilii to the hinder end of os ischii (i. e. the greatest length of the pelvis) in E. aculeata was 66 millim., the same distance in E. acanthion was 60 millim. only ; and whilst the greatest breadth (between the upper ends of ossa ilii) in E. aculeata was 44 millim., the same in E. acanthion is 41 millim. Also the foramen obturatorium was the larger in E. aculeata. The femur is shorter; in E. aculeata its length is 59 millim., in E. acanthion 53 millim. Any difference in the length of the |