62 BULLETIN 84, UNITED STATES NATIONAL MUSEUM. 



The material which is now in my possession has enabled me to make a more 

 detailed studj^ of A. otteri, and I am able to add a few complementaiy facts to the 

 characters already known for this species. I am satisfied that my determinations 

 are correct, for I have been able to compare the specimens of the United States 

 National Museum with the two types of Ljungman, which were most kindly com- 

 municated to me by Professor Thecl. 



The characters of the upper face of the disk are sufficiently well known. I have 

 given a drawing of that face, which, no doubt, is schematic, and I reproduce here 

 photographs of one of Ljuugman's types, neither of which is, unfortunately, in 

 a perfect state of preservation (pi. S, figs. 5 and 6). The radial shields of this are 

 elongated and fairly thin, but in the large specimens of the Albatross, as in those 

 from station 283S, they are much wider. The under face is covered in the inter- 

 radial spaces with plates which, in the larger specunens, are extremely thick and 

 strongly imbricated, so much so that they arc more or less obhquely erect. 



In Ljungman's type, a photograph of which I give on plate 8, fig. 6, the 

 mouth shields are noticeable through the presence, on the middle of their distal side, 

 of a very well-shaped, wide, and rounded lobe, which strongly protrudes in the 

 interradial space. Ljungman had simply said about it: "scuta oraha quadi'angula 

 margiuibus adorahbus convexis marginibusque aborahbus cxcavatis." In short, 

 these shields are a little longer than mde and their chief triangular part is followed 

 by a wide and protruding distal lobe. I do not find exactly that shape in the 

 specimens which were sent to me by the National Museum, or, at least, I find 

 some variations which I think should be noted. In the best preserved specimen, 

 from station 898 (Chesapeake Bay) and which I have represented in plate 8, fig. 7, 

 there is also a very large distal lobe, and therefore the shields are a Httlo longer than 

 wide, almost lozenge-shaped, with a rather obtuse proximal angle and a strongly 

 rounded distal angle. In the other specimens the distal lobe is confused with 

 the rest of the shield; the latter consequently shows an ovoid form and is longi- 

 tudinally elongated, with rounded proximal and distal angles ; sometimes the latter 

 angle is somewhat truncated so as to form a little distal edge. However, on the 

 smaller specimen from station 2838 (diameter of the disk, 10 mm.), the mouth shields 

 again display a chief portion which is triangular and a distal lobe which is wide and 

 distinct. The shape of the mouth shields observed on Ljungman's type does not 

 seem to me to be maintained in a very constant manner, and the distal part may be 

 more or less confused with the rest of the shield, instead of forming a distinct lobe. 



The shape of the external oral papilla has been correctly indicated by the 

 authors and it is always found with the same characters : strong, conical, elongated, 

 and obliquely erect. 



The ai'ms are extremely long and rather flattened. The upper brachial plates 

 are very large and triangular. On Ljungman's type they display a very obtuse 

 proximal angle and a strongly convex, sinuous distal side, which forms in its middle 

 a rounded and more or less conspicuous sweUing (pi. 8, fig. 9). It is perhaps not 

 cjuite accurate to say that these plates are "late quadrangula anguhs rotundatis 

 margiuibus aborahbus excavatis, adorahbus convexis." A rather neighboring shape 

 is observed on the two specimens from station 898, but the distal edge is simply 

 convex without the little median swelling, the proximal angle is strongly obtuse, 



