The Anatomy of Chlamydoselachus 427 



branchial chamber: and in one case, which I regard as anomalous since the external 

 spiracular opening is very much larger than the others, the spiracular canal is absent. 



In specimen No. I a bristle inserted into either external spiracular opening passes 

 anterolaterally, within the spiracular canal, to enter the pseudobranchial chamber. The 

 distance from the external spiracular aperture to the pseudobranchial chamber is about 

 10 mm., on each side. In specimen No. II, on the right side, a bristle inserted into the 

 spiracular canal by way of the external spiracular aperture travels about the same distance 

 and in a similar direction, before reaching the pseudobranchial chamber. In specimen 

 No. Ill, on either side, only a very slender bristle could be inserted by way of the ex- 

 ternal spiracular aperture, and this passed directly forward for a distance of about 5 mm. 

 before entering the pseudobranchial cavity. By dissection I have opened the spiracular 

 canals of specimens I, II, and III without finding anything of interest save a confirma- 

 tion of my description based on exploration with a bristle. Their walls are smooth. 



The spiracular canal always lies just beneath the integument. Thus the external 

 spiracular aperture is bordered, on the side toward the canal, by a somewhat flexible 

 lip. In cases where the external opening is large enough to allow the passage of an 

 appreciable amount of water, this lip may function as a valve preventing the intake of 

 water through the spiracle while the pharynx is expanding. In my four preserved speci- 

 mens the entire spiracular canal is very much flattened, since it is compressed between 

 the hyomandibular cartilage and the integument. 



In the free-swimming sharks, the spiracles are not so highly speciali2;ed for purposes 

 of respiration as in the skates and rays, which are bottom-dweUing forms. Concerning 

 the function of the spiracles, Daniel (1934, p. 156) writes as follows: 



In the free-swimming sharks the current enters the mouth, from which it passes into 

 the pharynx and into the gill-pockets, the external clefts, including the spiracle, at the same 

 time remaining closed. The mouth then closes, the external clefts open, and the water is 

 forced out. 



In the rays, which spend most of their time at the bottom and hence often in mud or 

 sand, there is an interesting change in the direction of the current. In these the greater part 

 of the current enters through the [large] spiracles and but little through the mouth. The 

 valves of the spiracles then close and the water is forced out ventrally through the external 

 branchial clefts. At the expulsion of the water the mouth does not entirely close, but only 

 a little of the water is able to gain exit through it because of valves which are located on its 

 roof and floor. 



In Squatina, a bottom-dwelling shark, the respiratory current is known to enter 

 through the spiracles (Darbishire, 1907), though not exclusively (Daniel, 1934). From 

 my observations on the structure of the spiracle in Chlamydoselachus it is obvious that 

 this organ normally functions as in the free-swimming sharks and not as in Squatina. 

 From the small si2;e of the external spiracular openings in Chlamydoselachus it is evident 

 that very little water passes through them. 



