igog.] R. E. Lloyd : Deep-Sea Fish caught by the " Investigator." 175 



5. Disorderly and medium . . . . Type y. 



6. Disorderly and broad. 



Of these six possible types no less than five are present in the collection. The only 

 one not represented is the broad disorderly type. 



Description of Types and Individuals. 



The types z and v are most unlike one another and will be described first. 



Type V ( disorderly and narrow ) — 



This is the species M. lutea in the strict sense. It occurs in three of the commu- 

 nities and will be found in the plate under the designation A i, 2; B 4; C i. The 

 four specimens resemble one another very closely. A i shows a tendency, however, 

 towards the opposite type in one respect. The ventral surface in front of the pelvic 

 fins, although covered with many platelets, shows one plate which is larger than the 

 others and is surrounded by five others. Behind the ventral fins, however, the 

 arrangement is quite disorderly. B 4 also shows a similar tendency. The suboper- 

 cular spines of A 2 and B 4 sho a^ some approach to the tetrafid type which is part 

 of the orderly character. B i and C i, although occurring in different communities, 

 show obscure pigmented rings on the upper surface, such as happens to come out well 

 in the photograph of C 4, on the right side of middle line. 



Type z ( orderly and broad ) — - 



This type has been described as M. triangularis. There are two specimens, D 2 

 and 5, occurring in the same community. The plate shows clearly that in the ordinary 

 acceptance of the word these two individuals are of a different species from M. lutea. 



Type X ( orderly and narrow ) — 



This is represented by the single small specimen A 4, one of the most interesting 

 fish in the collection. It can be seen that the disk is of exactly the same shape as 

 that of M. lutea, while the plates are arranged as in M. triangularis. Although it is 

 much smaller than any of the five specimens of type v, its subopercular spine is 

 actually larger than in some of the members of that type, and is perfectly tetrafid. 



Although this fish is probably immature, there is no more reason for supposing 

 that it would lose the orderly arrangement of its ossicles and retain its shape and so 

 grow into a M. lutea than there is for supposing that it would retain the pattern and 

 lose its shape and become M. triangularis . 



Type y ( medium and disorderly ) — 



This is represented by two individuals, C 2 and C 4, occurring in the same com- 

 munity. The shape of the disk is not quite the same, though both have departed 

 from the narrow type. As regards the upper surface of the disk they approach the 

 orderly type. On either side of the mid-dorsal row of plates is an area of skin 

 covered with a few small scattered platelets. The postero-lateral spines also show a 

 slight tendency towards the tetrafid type, that is, in the direction of the orderly 



