PARKER: MALDIVE CEPHALOCHORDATES. 43 



These records agree fairly well with those tabulated for this species by 

 Punnett (1903, p. 363), from whose table the modes and ranges at the base of 

 Table I. are taken. 



Heteropleuron agassizii, sp. nov. 



Plate 2, Fig. 5. 



One specimen of this species was dredged in twenty-four fathoms of water at 

 Malandu, Miladummadulu Atoll. It is rather elongated, measuring 27 mm. 

 in length by 3 mm. in depth. The dorsal fin is of almost uniform height 

 throughout. From the anal region to a point a little in advance of the anterior 

 end of the nerve tube, it contains fin-ray chambers to the number of four or 

 five to a myotome. In the anterior and posterior regions these fail to reach 

 the free edge of the fin, but in the trunk region they meet the edge. The most 

 anterior three chambers are without fin-rays, which are present in all the more 

 posterior chambers to a point about midway between the atriopore and the anus. 

 From this point jjosteriorly, only faint traces of fin-rays are here and there ob- 

 servable, and even these disappear as the caudal region is approached. Never 

 more than one fin-ray is present in a chamber. Often in the anterior region 

 and sometimes posteriorly the fiu-rays may reach to half the height of the fin, 

 but in most places they are only about one-fourth this height. Anteriorly the 

 dorsal fin is continuous with the rostral. Posteriorly it passes into the simple 

 inconspicuous caudal fin which in turn is continuous with the ventral. The 

 ventral fin has much less height than that part of the dorsal fin opposite to it, 

 and is without fin-rays or fin-ray chambers. 



The myotome formula is 45 -|-15 -[- 10 = 70. 



The chorda is stout and almost reaches the anterior and posterior limits of 

 the body, projecting well beyond the myotomes in both directions. 



The nerve tube has a faint anterior eye-spot followed by & series of smaller 

 spots reaching from the third to the last myotome, and showing the usual ten- 

 dency to fall into two groups for each myotome. 



The gonads form a single series on the right side, and are twenty-four in 

 number. They extend from the seventeenth to the forty -first myotome. The 

 specimen is a female. 



The oral region is so contracted that it is impossible to be certain of the 

 number of preoral cirri; at least nine to a side are present. 



Heteropleuron agassizii is related to H. bassanum, and especially to H. mal- 

 divense. In length it is between H. bassanum (43 mm.) and H. maldivense 

 (22 mm.). The ratio of its depth to its length, one to nine, is almost exactly 

 that of H. bassanum, and less than that of H. maldivense, one to six. The 

 gonads, which in H. maldivense begin between the ninth and thirteenth 

 myotomes and extend to a point between the thirty-third and thirty-ninth, in 

 H. agassizii extend from the seventeenth to the forty-first. The caudal fin of 

 H. agassizii, though much like that of H. maldivense, differs strikingly in its 



