354 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



such S. sterea, S. sladeni, etc. ; it is better to say that their proxi- 

 mal extremity is closed, and that they are some distance from the 

 mouth slit. 



Whatever may be the conditions and the development of the mouth 

 pores, they never open into the mouth in the different species of the 

 genus Ophiura, taken in the broader sense. But it is evident that be- 

 tween the mouth pores of species like those of the first group which 

 I have cited above (S. sterea, S. sladeni, etc.) and those of the second 

 group which I have just mentioned (A. abcissa, O. imbecillis, etc.) 

 there are considerable differences, and these may furnish us with 

 good characters for the differentiation of the species ; but these dif- 

 ferences must be stated in precise and correct terms. Thus not only 

 will serious errors be avoided, but also differences of opinion and un- 

 certainties in interpretation such as have sometimes occurred. 



For example, H. L. Clark, in drawing up the key of the species of 

 Ophiura belonging to the variabilis group ('09, p. 295), observed 

 that I placed 0. insolita among the species in which the mouth pores 

 open into the mouth, but that that is in contradiction with my figure 

 of 0. insolita. In reality my figure is slightly schematic, and as for 

 the text to be correct I would have to say, as I have advocated above, 

 that the mouth pores are elongated, gaping at their proximal ex- 

 tremity, and very close to the mouth slit. I include a photograph of 

 the ventral surface of O. (Amphiophiura) insolita in which the exact 

 relations of the tentacle pores to the mouth slits may be seen *(pl. 84, 

 %. 9). 



In his descriptions H. L. Clark has also used the incorrect expres 

 sion " the mouth pores open (or do not open) into the mouth slits." 

 In different species described by him in 1911, for instance in O. lep- 

 toctenia ('11, pp. 51-52), O. quadrispina (p. 56), O. mpnostoecha 

 (p. 66), O. megapoma (pp. 79 and 80), 0. penichra (pp. 84, 85). 

 0. actacta (p. 86), etc., he says that the mouth pores open into 

 the mouth ; this statement is evidently inaccurate, and in these species 

 the mouth pores do not open into the mouth slits any more than they 

 do in S. sterea and S. sladeni or in A. insolita. 



In speaking of the first two species H. L. Clark declares that the 

 mouth pores do not open into the mouth, and yet they have as great 

 a development as in the species described by him which I have just 

 named. I may even add that in studying different specimens of 

 S. sterea and of S. sladeni the impression is often given that these 

 pores really open into the mouth slits, as may be seen in some of my 

 photographs (pi. 83, figs. 2, 4; pi. 84, fig. 1). The appearance of the 

 ophiuran which makes us say sometimes that the pores open and 

 sometimes that they do not open into the mouth often has to do with 

 the state of contraction or of relaxation of these pores when the 



