THE SESSILE BARNACLES. 295 



Victoria. C. ligusticiis De Alesstuidri, of the Italian Pliocene and 

 C. darwini Bosquet, of the upper Cretaceous of Vaels, Belgium, are 

 fossil species not known to me by specimens. All other described 

 species are in the United States National Museum and are noticed 

 below. 



With the exception of the Hawaiian C. herribeli^ all of the species 

 are small, rarelj^ exceeding 12 or 15 mm. in diameter, and more 

 often half that size. They are generally conic or depressed, but 

 sometimes cylindric. The opercular valves are deeply locked or 

 mortised together. The tergum never has a long or distinctly formed 

 spur. 



In many species of Chthamalus the terminal segments of the 

 second pair of cirri have one or several broad or lanceolate spines 

 with conspicuously' serrate edges, as in figures 82&, e. I have not 

 dissected enough individuals of any one species to determine the 

 value of these spines as specific characters. They may perhaps A^ary 

 with the age of the individual. They are somewhat similar to the 

 spines from the first two pairs of cirri of Mitella figured by Kriiger, 

 :nid supi^osed b}^ him to have a sensory function. This appears to me 

 doubtful. Throughout the Balanomorph cirripedes one often notices 

 that some of the spines become delicately pinnate toward the end, but 

 I have not noticed such a specialization of this structure in any genus 

 but Chthamalus. 



In the maxilla the spines are arranged in three groups: An upper 

 group of two or three large and several small spines, followed by a 

 notch; a middle group partly of rather large spines, and a lower 

 group of mainly smaller spines. The species differ among themselves 

 in the nun^ber and length of the hairs on the upper and lower borders 

 of the maxilla and in the shape of the spinose edge, but Avith a few 

 exceptions the maxilloe are a good deal alike throughout the genus. 



The mouth parts and cin-i of Chthamahis deserve a much more ex- 

 tended examination than I have been able to find time for. 



The modifications of the mandible, etc., may be found to give the 

 best characters for subdivisions of the genus, but its structure is 

 unknown in some of the species, so that I have been unable to use 

 these characters in the key to species. There are two main groups : 



I. Mandible having four teetli foUowed by an even, comblike row of narrow 

 spines, below which the lower extremity is trispinose. The upper tooth is 

 much larger than the other three; the third and fourth are usually bifid 

 at the tips. Spines of the lower extremity are usually unequal. 

 a\ Spines between the fourth tooth and lower point are very numerous, 

 uan-ow, find crowded. (See p. 303, fig. Md.) 

 &\ Cirrus iii with one ramus far longer and more slender distally than the 



other C. cirratus. 



b\ Rami of cirri iii not vei-y unlike: ('. HtrjJnfus, C. s. anf/ustitcrguin, C 

 fraffiUs, C. daUi, C. anisopoma, V. challciKjeri, C. scabrosus. 



