602 Bashford Dean Memorial Volume 



upper jaw has elongated beyond the vertical of the eye. The spiracle also has moved 

 forward and slightly upward, and is now in the vertical of the angle of the jaw. The 

 gill'Straps are still angulate backward at their dorsal and ventral extremities. The first 

 has the free edge irregular, as though it had been bitten. External filaments are found 

 in gill'openings 1-4, but are still lacking in the spiracle. The pectoral and pelvic fins 

 show little progress. The dorsal and anal fins, however, have grown larger. Contrary to 

 what was found in the 34'mm. embryo (Figure 23, plate II) the caudal fin is bent upward 

 but the soft parts of the fin seem little larger than they were in the 34'mm. fishlet. 



Ventral View. — The original drawing of the 39'mm. embryo in this aspect is also 

 268 mm. long. This portrayal (Figure 27, plate III) is very instructive when compared 

 with that of the head only of the 34'mm. fish in like aspect (Figure 24, plate II). The fore' 

 head is decidedly round. The edges of the olfactory pits are thickened, as if the valves 

 are beginning to form. The eyes in this aspect are still prominent. The mouth is stretch' 

 ing forward toward the snout. The lower jaw has taken on something of the form found 

 in the adult, and the upper jaw no longer has a fossa in the symphyseal region. The an' 

 terior part of the isthmus is broader in this embryo than in the 34'mm. embryo. The gill- 

 arches all bear external filaments, those of the first slit being especially long — longer than 

 they are shown in the lateral view (Figure 25), and longer than they are in the stages im- 

 mediately following. The hindmost right gill'Strap is curiously twisted. The stumpy 

 pectoral fins show no progress, but the pelvics are well developed and the cloacal eminence 

 appears between their hinder ends. Faintly outlined in the drawing is the ventral lobe 

 of the caudal fin.. 



Brief comparison of the 39'mm. Chlamydoselachus may be made with Scammon's 

 37'mm. Squalus. In the latter, the fins are better developed. On the head the nasal pits 

 are much more developed, and the latero-sensory canal system shows plainly. If present 

 on Chlamydoselachus is it not shown in the drawings. The mouth of the frilled shark, 

 however, is better developed. The embryonic gill'filaments of Squalus are profuse and 

 long, some still coming from the spiracles. In Chlamydoselachus they are present in the 

 gill'slits only, but are short and inconspicuous. 



The figures of the 37'mm. Squalus are the last of Scammon's drawings made of 

 specimens in the flesh. His other figures (text'figures) are reconstructions of serial 

 sections of these embryos (portrayed in his plates I-IV). Comparisons with the drawings 

 in his plates have been very instructive and helpful, and it is regretted that his series of 

 plate drawings does not extend to older and larger embryos. 



The 39'mm. Embryo and its Yolk Sac in Color 



Colored drawings were made of but three of Dean's Chlamydoselachus specimens — all 

 shown on Plate V. Fortunately one of these is of the identical egg of which detailed 

 figures have just been studied. This embryo and its yolk sac are beautifully portrayed 

 in Figure 50, plate V. The embryo measures 39 mm. in length and the yolk sac 95 x 65 

 mm. The yolk stalk averages about 2.5 mm. in width and is about 7 mm. long. This long 



