84 N, ODHNER: THE GENUS CUMANOTUS. 



remains the inner anatomy to be dealt with ; but here I considered it 

 unnecessary to compare the whole organization of the two forms in 

 detail, and I have accordingly only examined the organs that are 

 primarily of specific value, viz. the radula and the mandibulae. 



The rows of the radula in C. heaumonfi vary in number from 16 to 

 24, according to Eliot ; in C. laticeps I have found about 17. The teeth 

 are furnished in both forms with long, slightly curved cusps. The 

 form and the denticulation of the median tooth do not present any 

 differences. The lateral teeth are denticulated only on the inner sides. 

 In the latest formed part of the radula, 1 have found the number 

 of denticles of the laterals circa 25 in C. heaumonti and 18 in C. laticeps ; 

 in the older part above 25 and about 22 respectively. This slight 

 difterence is of no consequence, especially as the form and curvation of 

 the lateral teeth are the same in the two specimens examined. 



There remains only one more character to consider, the structure of 

 the mandibulae, but here too I have found entire agreement. Their form 

 and colour correspond, as do those of the whole bulbus pharyngeus 

 too. The mandibulae are lengthened, roundly quadrangular, and denti- 

 culated in the anterior margins. In the denticulation there exists but 

 a slight difference, the denticles seeming to be placed at somewhat 

 greater intervals in C. laticeps than in the other. As to the shape 

 of the denticles, I have found them in both forms to be somewhat 

 irregular, uni-, bi- or tricuspidate, the more complicated ones being 

 situated in the upper or anterior part of the jaw margin, a part which 

 is most worn. Tlie denticles are arranged in one row only at the 

 margins. Two specimens of each were examined. In these mandibular 

 characters also the forms agree wholly with one another. 



It has consequently not been possible to find out any specific dis- 

 tinguishing points between the two forms ; in all the characters they 

 are alike. I therefore consider their identity to be proved. Nor are 

 there any good reasons for their severance as varieties ; it is hardly 

 probable either that any would be obtainable from the characters 

 of the living animal, though the colouring might doubtless be subject 

 to some variation, as is usual with the Nudibranchs. 



As a result of the above comparison, I consider the genus Cumano- 

 tus to consist of one species only, viz. C. heaumonti (Eliot, 1906), 

 and regard my own species, C. laticeps, Odhner, 1907, as a synonym. 

 C. heaumonti consequently has a wide distribution, being obtained 

 in England as well as in Northern Norway. Further investigations 

 will certainly show its occurrence also in the intermediate districts. 



