THE GROWTH OF GROUPS 141 



those that are farthest apart. Malthopsis has not been 

 found elsewhere, although we are comparatively well 

 acquainted with the inhabitants of the deep seas on either 

 side of the Indian Peninsula. The numbers of in- 

 dividuals caught at the four stations are 10, 7, 4, and 5. 

 Of the first group I have examined only six, so that my 

 conclusions are based upon an examination of twenty-two 

 individuals in all. The reader will no doubt notice that 

 the conclusions are concerning a species ; that is, many 

 millions of individuals, out of which number twenty-two 

 representatives are taken at random for consideration. 

 Further, it will be obvious that we know nothing con- 

 cerning the parentage of one of them. 



It is necessary to describe briefly some of the external 

 features of Malthopsis. The body consists of a flattened 

 portion or disc which is triangular or heart-shaped, the 

 mouth being placed at the corner corresponding to the 

 apex of the heart. The paired fins are placed as in 

 the diagrams, Fig. 7. The skin is set with bony plates. 

 There are three prominent spines, one at each of the 

 three corners of the disc. The foremost or nasal spine 

 is placed just above the mouth. The others, which may 

 be called the lateral spines, project one on either side 

 from the outermost parts of the body. 



There is great variation among this collection of fish, 

 affecting two of their attributes, which appear to be quite 

 independent of one another. These attributes are the 

 shape of the disc and the arrangement of the dermal 

 plates. Regarding the former, we see that there are 

 three types ; a narrow, a medium, and a broad type of 

 disc. But if we disregard this and examine only the 

 arrangement of the dermal plates, we find that there are 



