THE SESSILE BAENACLES. 293 



fl'. Six compartments. 



b\ Rostrum liaving aire like the carina, the adjacent rostrolateral compart- 

 ment without al«-ou either side Chthaiiialus (p. 293). 



h^. Rostrum overhippinj? the adjacent lateral compartments, which have alte 

 on the rostral side. 

 c\ Basis calcareous. 



ri\ Compartments, except the carina, having distinctly differentiated 



radii IhilhtibnUinus} 



(/". Radii wanting or not distinctly differentiated from the parietes. 



rack j/lasiii a ( p. 327 ) . 



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



a\ Eight compartments at least. 



h^. Rostrum and rostrolateral compartments closely united by linear su- 

 tures Pachylasma (p. 327). 



b^. Rostrolateral compartments as distinct as the others; rostrum with aljB. 

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



Octomeris (p. 3.34). 

 c'. Wall surrounded with short accessory compartments outside. 



t'a iopli nigin us ( p. 334 ) . 



Genus CHTHAMALUS Ranzani. 



1817. Clitliamulus Ranzani, Opuscoli Scientifici, vol. 1, p. 27G (no species 



mentioned. ) 

 1S18. Chthamalus Ranzani, Opuscoli Scientifici, vol. 2. p. S3 (for C. glaber 



and C. steUatus). 

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



monotype E. licmbcli. 

 18-54. ChtJiamoIits Ranzani, Dakwin, Monograph, p. 447. 



Compartments six; rostrum similar to the carina in being provided 

 with ala_^; rostrolaterals triangular, without alte, the sheath having 

 a narrow projection. Carinolatcrals wanting. Basis membranous 

 or covered with a calcareous laj-cr 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 spinosc, the third pair much longer and bearing spines like 

 those of the later pairs. 



Type. — Chthamalus steUatus (Poll). 



Dlstrihution. — Nearly world wide, in the littoral zone. 



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

 subfamil}^ of the Chthamalidse, distinguished by the persistence of 

 the rostrolaterals as distinct compartments and the loss of carino- 

 laterals. It differs essentiallj^, therefore, from other hexamerous 

 Chthamalidse, in which the rostrolaterals are concrescent with the 

 rostrum, and the carinolaterals persist as separate compartments. 

 The shape of the rostrolateral compartments, Avhich have no ala^, 

 is extremely characteristic of the genus (pi. T3, fig. 2c; pi. 75, fig. 1). 



1 This genus is not contiiined in tlic United States National Museum. 

 4729°— Bull. 93—10—20 



