1830.] PROF. F. J. BELL ON THE TEMNOPLEURID.E. 437 



in other points they are almost exactly alike. Is it possihle that 

 they are different sex-forms of the same species ? 



3. Amblypneustes formosus. 



Capt. Hutton states (Trans. New-Zealand Inst. ix. p. 3'j2) that 

 his E. elevatus (Catal. N.-Z. Echiuodermata, p. 11) is synonymous 

 with this species. 



There are, as is well known, a niimher of specimens of this species 

 to which it is easy enough to allot their place, and the only diffi- 

 culties which arise are those which are consequent on the close 

 affinity of the species A. pallidus. 



What is of especial interest to note is that here, just as in the 

 forms united ivnder the head of A. griseus, there are two very 

 distinct sizes of the genital pores ; the distinction is obvious enough 

 when a few specimens are carefully observed ; but there is no great 

 difference in the moderately-sized madreporic plate, nor can I arrive 

 at any definite correlation of differences in proportion, similar to 

 those already noticed in A. griseiis. It is to be hoped that natu- 

 ralists, who are enabled to get their specimens fresh, will be able to 

 discover with what difference, if any, in the characters of the genital 

 organs this difference is connected. I have been anxious to find 

 some means of expressing this difference : — first, for the purpose of 

 affording a standard to those who are also working at this subject ; 

 and, secondly, for the purpose of presenting the difference in rela- 

 tions distinctly to the minds of those who take a less special interest 

 in the matter. By the kindness of a colleague I was provided with 

 four entomological pins of different sizes ; the most delicate was 

 almost exactly half the diameter of the strongest ; their numbers, 

 for which neither he nor I are responsible, are respectively 2, 17, 

 14, 16. No. 2 is the most delicate, and no. 14 is thicker than no. 17 ; 

 and no. 16 is the thickest, and is rather more delicate than an 

 ordinary toilet-pin. 



i. A specimen measuring 34"5 millims. in diameter just allowed 

 the insertion of pin 16 into one of the genital pores. 



ii. A specimen measuring 35" 1 millims. in diameter was injured 

 by pin 1 7. 



iii. A specimen measuring 28 millims. would only admit the tip 

 of pin 2. 



iv. A specimen measuring 20'5 millims. easily admitted pin 17, 

 and just refused 14. 



v. A specimen measuring 21 millims. only admitted just the tip 

 of pin 2. 



Two series are therefore quite evident. 



Prof. A. Agassiz has directed attention by his figures to the 

 depressed and oviform varieties of the test ; the succeeding Table 

 illustrates this well enough, as it shows that the height may be only 

 84*1 or as much as 102 per cent, of the diameter of the test; the 

 three other specimens present, however, a very striking similarity in 

 proportion. 



29* 



