M. R. Leuckart on the Young States of some Annelides. 259 



3. Rhynchonella psittacea was moderately abundant in the 

 extreme north, from Tromsoe to the North Cape, in a living state, 

 in 70 to 150 fathoms water. Dead valves 



were found at Hammerfest in mud. I found 

 Rhynchonella very difficult to examine, the 

 animal being extremely timid and closing 

 its valves on the slightest movement. The 

 coiled arms are extended, so that the cirri 

 when unbent come as far as the margin of Rhynchonella psittacea. 

 the shell. I have frequently seen this spe- 

 cies with its valves open, but it never protruded its arms. 



4. Crania anomala, Miill. 

 sp., was met with between 

 Drontheim and Tromsoe, at- 

 tached to stones, shells, &c., 

 in 40 to 150 fathoms water; 

 the cirri are protruded, but 

 not the arms, beyond the mar- 

 gin of the shell. The valve 

 opens by moving upon the 

 straight side as on a hinge, 

 without sliding the valve. Crania anomala, Miill. sp. 



XXIV. — On the Young States of some Annelides, 

 By R. Leuckart *. 



[With a Plate.] 



In his copious " Observations on the Anatomy and Development 

 of some Invertebrate Marine Animals,^^ Busch has figured (pi. 8. 

 figs. 1-4) the larva of an Annelide of unknown origin, which is 

 particularly remarkable in many respects, and especially from 

 its possession of strong spines and fringes of cilia upon the in- 

 dividual segments. In the spring of 1853 I not unfrequently 

 took similar larvae from the surface of the sea near Nice and 

 Villa Franca. The stage of development in which they occurred 

 agreed pretty well with that observed by Busch, at least in most 

 of the specimens : younger larvse were never found, but some 

 occurred which had proceeded a little further, and these proved 

 their increased development especially by the partial or even 

 complete loss of the above-mentioned spines. When the tem- 

 porary nature of this peculiar apparatus of bristles was esta- 

 blished, it was tolerably easy, by the consideration of the other 



* Translated by W. S. Dallas, F.L.S., from Wiegmann's Archiv, 1855, 

 p. 63. 



