136 SPIONIDS. 



of long swimming-bristles, paratroch, and telotroch. He also describes and figures a 

 Nerine larva, and a stage of Magelona. His youngest larva of the Spionidae is furnished 

 with a pair of provisional bristles. He gives an elaborate scheme of the pigment-specks 

 on the head and body of this group. 



Mesnil l (1896) in his important treatise on this family observes that in each setigerous 

 lobe the bristles are in two rows — anterior and posterior — and he points out that the other 

 Spionidae differ from Spio and Scolecolepis in various characters, such as (1) the disappear- 

 ance of the branchiae — 



(a) From the first setigerous segment. 



(b) From a certain number of the anterior segments. 



(c) From a great number of the posterior segments. The latter (c) may exist along 

 with a and b. 



(2) A cup-shaped expansion round the anus formed (he says) by the coalescence of 

 the anal cirri. 



(3) After a certain segment the posterior row of dorsal bristles includes winged 

 hooks like those in the ventral division. 



(4) The anterior ventral row of capillary bristles remains as well as the winged 

 hooks. Sometimes the same occurs in regard to the inferior ventral bristles. 



Mesnil also notes that besides Scolecolepis there are a few other Spionids in which 

 the prostomium presents two frontal horns. Thus the species which Wiren reported as 

 Nerine vulgaris, Johnston, and Scolecolepis sp., Marenzeller, present modifications 1 a 

 and 3 " on ne suit rien sur les appendices anaux." They constitute Mesnil's new genus 

 Marenzelleria. 



He gives the following key : 



I. Prostomium without frontal processes. 



Fifth setigerous segment J Branchiae after the fifth setigerous segment Polydora. 



modified I Branchiae on the second setigerous segment Boccardia. 



Branchiae on first setigerous f Vanishing on the first region of the body . Laonice. 



segment I Continuing to the posterior end . . Spio. 



, T . t , t [Anal cirri . . . Microspio. 



JN o winged hooks on 



, , n . . . ^Anal region cup- 



dorsal division _ _ A ^ _ . . _ 



shaped . . . JNermides. 



Winged hooks in /Anal cirri . . . Aonides. 



dorsal division I Anal cup . . . Nerine. 



Branchiae after second seti- r Dorsal lamella independent of branchia . Spionides. 



gerous segment I Dorsal lamella soldered to branchia . . Pygospio. 



II. Prostomium with frontal processes. 



Branchiae on first setigerous r No winged hooks in dorsal division . . Scolecolepis. 



segment 1 Winged hooks in dorsal division . . Marenzelleria. 



The author makes many interesting observations on the morphology of the Spionids. 



Thus the feet have a dorsal and a ventral lamella behind the setigerous process, and 



besides the dorsal and ventral bristles some have a small fascicle more ventrally situated. 



The youngest bristles are in the dorsal situated ventrally, and in the ventral dorsally. The 



1 < Bull. Sc. France et Belg./ t. xxix, pp. 110—287, pis. vii— xv, 1896. 



Branchiae on second seti- 

 gerous segment 



