604 Bashford Dean Memonal Volume 



of this embryo is compared with that of the 39'mm. specimen m the same view, it is 

 seen that the larger embryo has a rounder and shorter snout with eyes somewhat 

 less prominent and more normal. There are faint traces of the sensory canal system on 

 the head. The spiracles are smaller, and are more dorsally situated — higher on the 

 head. The gill-flaps are more widely distended than those of the smaller specimen. The 

 external gill-filaments, lacking in this view in the 39-mm. embryo, are very noticeable 

 especially in the first, second and third slits, and a few short ones are even tound projecting 

 from the spiracles. Both paired and median fins are better differentiated than in the 39- 

 mm. embryo, and the artist has been able to portray m outline the dorsal fin and the soft 

 dorsal part of the tail fin. 



Lateral View. — Comparison and contrast will now be made ot the 46- and 39-mm. 

 embryos as seen m side view in Figure 29, plate III. and Figure 25, plate II. Where the 

 39-mm. fish is almost straight from head to dorsal fin, the 46-mm. fish has a depression in 

 the vertical of the spiracle and angle of the mouth. Back of this the little fish is very 

 sway-backed clear to the dorsal fin. The head ot the 46-mm. specimen is shorter and more 

 flatly rounded. The depth of the head is noticeably less than that of the 39-mm. fish. 

 The nasal aperture is greatly reduced. Eye and mouth are both closer to the end of the 

 snout, and the eye is very large. The spiracle is now a narrow sHt seemingly not placed so 

 high as it is shown in the dorsal view of this 46-mm. embryo. The first gill-cover seems 

 either distorted or anomalous, unduly exposing the filaments of the first demibranch. The 

 39-mm. embryo has only short gill-filaments but m the 46-mm. specimen all the slits, but 

 especially the first, have a profusion of slender external filaments — there are two projecting 

 even from the spiracle. The paired fins are better developed than those of the younger 

 specimen. Likewise dorsal and anal fins show much growth. Note that they look cut 

 off squarely behind. The caudal fin is sharply bent down but the soft parts are devel- 

 oping Vi'ell. 



Ventral Aspect. — Seen from below (Figure 30, plate III), the 46-mm. embryo is very 

 much like the 39-mm. one (Figure 27, plate IIIj. The head is narrower and more rounded. 

 This brings the nasal capsules and eyes closer to each other. The mouth has elongated 

 somewhat. There is a remnant of a fossa in the median part ot the upper jaw. This jaw is 

 more heavily built and more sharply outlined than that ot the younger fish. The mouth 

 is still widely open and the lower jaw noticeably approaches the form of that ot the 

 adult. The gill-arches are widely distended and bear a profusion ot external filaments. 

 The isthmus is very narrow and the first pair of gill-covers is confluent over it. Thus 

 first of all this embryo of 46-mm. justifies the name assigned this shark — Chlamydoselachus, 

 the cloak-gilled shark. Lastly, the paired fins are much more developed than those of the 

 39-mm. specimen, and the cloaca shov^-s conspicuously between the tips of the pelvics. 

 The artist has also been able to show the anal fin and the lower lobe of the caudal. 



The head of this 46-mm. embryo in both dorsal (Tigure 28, plate III) and ventral 

 (Figure 30, plate III) aspects seems entirely normal. But portrayal from the side shows 

 a head which seems abnormal in every respect (Figure 29, plate IIIj. One almost doubts 

 'if the three drawings were made from the same embryo. 



