LOCOMOTION OF DENDRONOTUS GIGANTEUS. 259 



esting to note that locomotion in this echinoclerm is in essentials of 

 that type of gastropod locomotion which has been designated the 

 direct monotaxic type. 



Olmsted ('17) finds in the huge slug Veronlcclla schivclyoe 

 Pilsb. there are always about eleven pedal waves which pass from 

 the posterior to the anterior and extend the full width of the foot ; 

 this is direct monotaxic locomotion. In Onchidium floridanum 

 only one or two waves are shown at a given time. In Eulota 

 smmlans Per. the average number of waves are 9 a 10. Helcinia 

 convexa Pfr., Tcthys dactylonula Rang, and Fissureila nodosa 

 Born show retrograde monotaxic locomotion. Tectarius misri- 

 catus L. exhibits retrograde alternate ditaxic locomotion. Trito- 

 nidca tincta and Columbclla mercatoria L. are retrograde tetrataxic 

 in their locomotion. Cyprcea exanthema L. shows long and short 

 lateral waves which move either to the right or left; complete 

 diagonal waves which move to the right or left, and retrograde 

 waves from the anterior edge to the center of the foot and extends 

 to the posterior. Finally, Marginclla arena Val., Hammea antil- 

 larum Orb., and Bull a ocddentalis A. Ads. move by ciliary action 

 alone. Retrograde pedal waves, according to Crozier ('19), are 

 the means of locomotion in Ischnochiton purpurasccns Ad., Acan- 

 thochitcs spiculosus Reeve, and Tonicia sp. ; the first-named one 

 also exhibits a "gallop" like that of Helix, which is independent 

 of the pedal waves. 



The remarkable nudibranch Dcndronotus gigantcus has recently 

 been described (1921) from the Vancouver Island region by Dr. 

 Chas. H. O'Donoghue. This author records four species of this 

 genus: D. arborcsccncc Muller, D. dalli Bergh, D. giganteus 

 O'Donoghue, and D. rufus O'Donoghue, from this region. The 

 largest of these species measured : 50 mm. long by 15 mm. high by 

 15 mm. broad; 31 mm. by 9 mm. by 6 mm.; 140 mm. by 43 mm. 

 by 33 mm.; and 14 mm. by 4.5 mm. by 4 mm., respectively. Ac- 

 cording to this author, a preserved specimen of D. gigantcus in the 

 laboratory obtained by Professor C. M. Fraser, 1913, measured 

 210 mm. long by 84 mm. high by 55 mm. wide. Allowing for 

 approximately the same amount of shrinkage, according to O'Don- 

 oghue, the specimen when alive must have reached the size of 260 

 mm. long by 100 mm. high and 65 mm. broad. This is indeed a 



