THE SESSILE BAENACLES. 293 



a . Six compartments. 



l> 1 . Rostrum having nine like the carina, the adjacent rostrolatcral compart- 

 ment without al;i> on either side ChtJi<iialits (p. 293). 



& J . Rostrum overlapping the adjacent lateral compartments, which have ahe 



on the rostral side. 

 c 1 . Basis calcareous. 



d\ Compartments, except the carina, having distinctly differentiated 



radii Bathijbalnnus> 1 



il". Radii wanting or not distinctly differentiated from the parietes. 



Pa ch yhisin a ( p. 327 ) . 



c 3 . Basis membranous, at least in the center ; no radii Hexelasma (p. 329). 

 a 3 . Eight compartments at least. 



I) 1 . Rostrum and rostrolateral compartments closely united by linear su- 

 tures Pachylasma (p. 327). 



I 3 . Rostrolateral compartments as distinct as the others ; rostrum with ate. 

 c\ No accessory compartments outside the eight composing the wall. 



Octomeris (p. 334). 

 c 2 . Wall surrounded with short accessory compartments outside. 



Catophragmus (p. 334). 



Genus CHTHAMAL.US Ranzani. 



1S17. ClitJiamalus RANZANI, Opuscoli Scientific!, vol. 1, p. 270 (no species 



mentioned. ) 

 1818. Chthamalus RANZANI, Opuscoli Scientific!, vol. 2, p. 83 (for C. tjlabcr 



and (7. stellatus). 

 1837. EurapJiia CONRAD, Journ. Acad. Nat. Sci. Philadelphia, vol. 7, p. 261, 



monotype E. hcinbcJL 

 1854. Chthamalus Ranzaui, DARWIN, Monograph, p. 447. 



Compartments six ; rostrum similar to the carina in being provided 

 with alfe; rostrolaterals triangular, without alee, the sheath having 

 a narrow projection. Carinolaterals wanting. Basis membranous 

 or covered with a calcareous layer formed of the inflected basal edges 

 of the compartments. 



Labrum with the concave or straight edge toothed or hairy. Man- 

 dible with the lower part pectinated. First two pairs of cirri short, 

 densely spinose, the third pair much longer and bearing spines like 

 those of the later pairs. 



Type- Chthamalus stellatus (Poli). 



Distribution. Nearly world wide, in the littoral zone. 



Chthamalus is one of the most distinct genera, really forming a 

 subfamily of the Clithamalidae, distinguished by the persistence of 

 the rostrolaterals as distinct compartments and the loss of carino- 

 laterals. It differs essentially, therefore, from other hexamerous 

 Clithamalidae, in which the rostrolaterals are concrescent with the 

 rostrum, and the carinolaterals persist as separate compartments. 

 The shape of the rostrolateral compartments, which have no alse, 

 is extremely characteristic of the genus (pi. 73, fig. 2e; pi. 75, fig. 1). 



1 This genus is not contained in the United States National Museum. 

 4729 Bull. 9316 20 



