The Jiatural History of the Frilled Shar}{ 283 



We, like others before us, have pointed out certain superficial resemblances between 

 Chlamydoselachus and an eel, but Dr. W. K. Gregory, in a personal communication to 

 the writers, comments on this matter as follows: 



Chlamydoselachus differs profoundly from all eels in the possession of large well de- 

 veloped flat pelvic fins, of stout shark-like pectoral fins and of a heterocercal tail utterly unlike 

 the gephyrocercal tail of eels. The cross sections of its head and body differ widely from those 

 of eels. Therefore I cannot believe that its motion is especially eel-like. Its vertebrae are 

 utterly different from those of eels and therefore unfavorable to the extreme flexure of the 

 body. The musculature of Chlamydoselachus is thoroughly shark-like and it seems to me 

 that the eel-analogy has been greatly overdone in the literature and that it is simply an elongate 

 shark in movements as in anatomy. 



TROPHIC FOLDS 



These curious structures, found in no other shark so far as we know, were first 

 described by Garman (1884.1, p. 51) in his 1511'mm. female fish as follows: "Under the 

 middle of the belly, the skin forms two closely approximated rolls or ridges separated by a 

 groove, and inside of these the muscle is thicker than toward the flanks." Garman for the 

 same fish (1885.2, p. 3 ) again refers to the fact that "A prominent doubled or grooved keel 

 along the median line of the belly adds considerably to its depth. Toward the pectoral 

 arch and the pelvics the keel loses its prominence. It is largest near the middle of the total 

 length, where it projects three-quarters of an inch, and the groove has a depth of one- 

 third as much." Garman found these folds on his second (female) specimen (1887), but 

 the only other investigators who have noted them are Collett (1897), who found them 

 Very indistinct" in his (1910-mm). female specimen, the largest but one ever captured; 

 and Braus (1898) who studied the innervation of the muscles of this region and concluded 

 that the groove between the folds is formed by an infolding of the body-wall. 



We have examined all our specimens for these folds and present the following find- 

 ings. Our fish No. II (a female, 1485 mm. long) shows only a trace of the folds reaching 

 from the middle point of the abdomen for about 125 mm. (5 in.) forward. This fish has 

 been split down the center line of the belly, and we at first thought that this had obliter- 

 ated the folds. But had this slit been made along the groove, the elevations would show 

 on either flap. However, our fish No. I (1350 mm.), also a female, shows these folds well 

 developed. They extend from about a line joining the posterior edges of the bases of the 

 pectorals backward 340 mm. (13.3 in.) to a point about 25 mm. (1 in.) in front of the bases 

 of the pelvics. This fish has been split open to the left of the folds and the right abdominal 

 wall is very much crumpled, which may in part account for the shallowness of the anterior 

 fourth of the groove; back of this, the groove is quite uniformly 4 mm. in depth except at 

 the end where it shallows out. Finally, our largest fish (No. Ill, 1550 mm. long), also a 

 female, has had the ventral wall split to the right of the tropeic folds. These extend from a 

 line joining the middle parts of the pectorals backward 385 mm. (15.1 in.) to flatten out 

 about 45 mm. (1.75 in.) in front of the bases of the pelvics. The groove varies from about 

 2 mm. to about 4 mm. in depth. It should be borne in mind that all our measurements are 



