76 



The genera Temnopleiiriis and Salmacis are verj' nearly related, so nearly 

 indeed that it seems impossible to find any character distinguishing between them 

 with full certainty. To be sure Duncan '■) has found in Temnopleurus only 4 parts 

 in the „rosette" of the sucking disk, in Salmacis 6—7 parts. This would give an 

 easily accessible character distinguishing these two genera, but unfortunately it does 

 not hold good. In all the Temnopleurus- and Sa/macis-species I find the number of 

 these plates to be 4—5, rarely 3 or 6. In T. Reevesii I have found only four, in S. 

 dussumieri only five, but I do not doubt that in these species also the other num- 

 bers may occur. — The pedicellariæ and spicules do not alTord generic characters 

 here and so cannot be used for distinguishing the genera. Thus only the well 

 known characters in the structure of the test are left for the distinction of the two 

 genera, but none of these characters are exclusive. Temnopleurus has large grooves 

 in the test, Salmacis only small pits: but S. Alexandri is almost like Temnopleurus 

 and T. Reevesii almost like Salmacis in this respect. Temnopleurus has few series of 

 tubercles, Salmacis has several series, both vertical and horizontal ; but large speci- 

 mens of Temnopleurus have also more (6) series of interambulacral tubercles, 

 arranged likewise in horizontal series, and young specimens of Salmacis have few 

 series of tubercles as Temnopleurus. The form of the test is generally high in 

 Salmacis, low in Temnopleurus, but S. dussumieri is as low as any Temnopleurus. 

 Both ringed and uniformly coloured spines occur in both genera; also the buccal 

 membrane is alike in both of them. There is thus not a single character which 

 distinguishes sharply betw'een the two genera. It will, however, be practical to main- 

 tain both the genera; it will scarcely ever be difficult to decide to which of them 

 any species has to be referred. It is the two species T. Reevesii and S. dussumieri 

 (together with the var. S. Alexandri) which cause the difficulties; if these two species 

 were removed from the genera there would be excellent characters distinguishing 

 Temnopleurus and Salmacis; only the xar. Alexandri, which cannot be excluded from 

 the geuus Salmacis on account of its evident near relation to S. virgulata, will 

 remain as a form intermediate in characters between the two genera. The two 

 above named species would then have to be made the types each of a separate 

 genus, as it would be impossible to unite them into one genus. This might not be 

 unreasonable. The name Toreumatica Gray should then be used for Reevesii, 

 whereas the name Diploponis Troschel might be used for dussumieri. I do not feel 

 sure, however, which is the better arrangement, and for the |)resent I leave these 

 species in the genera, where they have been placed for so long a lime, and with 

 which they are evidently most nearly related. 



') On the Anutomy of the Teranopleiiridæ. Ann. Nat. Hist. 6. Ser. I. 1888. p. 127. 



