272 SIR C. ELIOT ON N UDUiRANCHS [NoV. 29,. 



one specimen being as much as 25 centimetres long and 16"5 

 broad. It is very active, swims rapidly, and has been found on 

 the surface of the sea a quarter or half a mile from the shoi-e. 

 The colour of the doi'sal surface within the borders is very 

 vaiying and may be bright light-red, oi-ange, yellow, sandy, 

 almost white, or still more fi-equently mottled with all these 

 colours. Sometimes the external red border is divided into two 

 pai'ts by a lighter line as in the last vai'iety. The branchise 

 exhibit somewhat similar variations of colour, but are generally 

 of a pale reddish yellow with dai'ker lines on the axes and 

 white tips to the pinnae Sometimes the main axes are bright 

 light green. 



I have been unable to find any differences of structure between 

 these three varieties : faustus, marghmtus, and moehii. In all 

 the radula consists of from 30-45 rows of simply hamate teeth, 

 rather slender, 65-80 on each side of the naked rhachis. The 

 branchife are from six to eight, seven being perhaps the commonest 

 number. Each so-called branchia consists, as a rule, of four 

 plumes (but sometimes of three or five) inserted very close 

 together but not springing from a common stem. Not unfre- 

 quently one plume is separated a little from the others, and the 

 individual then appears to have an abnormally large numbei- of 

 branchiae. 



DORTDOPSIS. 



This genus is distinguished from the other cryptobranchiate 

 Doi-ids by having a suctorial buccal apparatus, with no jaws or 

 radula. The mouth is a fine pore situnted in the anterior part of 

 the foot ; and the internal organs consist of a buccal cone from 

 which issues a long tube which is generally twisted and expands 

 into a dilatation before entering the liver. Beneath the anterior 

 pai't of the tube is a large foUiculate mouth-gland, generally 

 double. The true salivary glands appear to be i-epresented by 

 two nodules at the commencement of the dilatation. The nervous 

 system is very concentrated. The liver is bifid behind. There is 

 an armature of minute hooks on the spermatic duct and glans. 

 On the upper wall of the pericardium are a number of Inmellte, 

 sometimes called the pei-icardial gill. The animals are generally 

 soft, more rarely spiculous, either smooth or tuberculate. The 

 branchife are rather large and few (rarely more than 8), and 

 though they are completely retractile, are very commonly ex- 

 serted in preserved specimens so as to appear at first sight non- 

 retractile. This feature seems to depend on some peculiarity of 

 texture, and not on any difference of structure. 



The genus is very abundant in the Indo- Pacific, and about 

 60 species have been described, many of doubtful validity. Even 

 in dealing with the forms Avhich are adequately described, it is 

 not easy to draw the line between species and varieties, as neai'ly 

 all are very variable both in shape and colour, and the internal 

 organs present few features which can be safely used for classi- 



