82 BULLETIN 60, UNITED STATES NATIONAL MUSEUM. 



Genus PCECILASMA Darwin. 



1851. Pcpcilasma Darwin, Monograph on the Cirripedia, Lepadida', p. 99, first 



species P. l\rv}])feri. 

 1884. Temnaspis Fischer, Bull. Soc. Zool. de France, IX, 1884, p. 357, for P. 



Jissa Darwin. 



Capitulum of five fully calcified approximate valves, the umbonos of 

 sciitii and carina basal; carina not extending between theterga, narrow 

 throughout. No lateral filaments at bases of the cirri; caudal append- 

 ages one-jointed, spinose. Cirri ii to vi with 4 or 5 pairs of long 

 spines on the anterior side of each segment. 



T>/pe. — P. 'ksempferi. 



The discovery of new forms has materially enlarged the group of 

 pentaspidian barnacles of the Pcecilastna type since Darwin's time, 

 and some notes on their classification and nomenclature may be in 

 order. The oldest generic name for a species of the series is Trilasinls 

 Hinds, based on T. ehurneum Hinds. If we consider this species to 

 be a Pmcilasma, then the name TrUasvds must replace P<ec!h(.wia^ 

 since it is anterior in date. In a former paper I admitted both groups 

 as genera, thinking the peculiar structure of the carina of Trilasmis 

 justified this course.'* It must be conceded that T. ehurneum does not 

 difi'er from Pwcilasvta much more than Lepas fascicular is from the 

 other species of Lepas; j^et I think no advance in our conceptions 

 would result from merging Pa^cilasma in Trilasmis. but rather the 

 reverse. 



Pcecilas'iaa^ after the elimination of Trilasmis, still contains very 

 diverse species, and those like 7^. carinafaz/t, P. rectum .^ etc., with the 

 carina enlarged basally, should probably be separated from I\ecilasina 

 and united to Megalasma as a subgenus. For the present I erect a 

 subgenus Glyptelasma for them. This group stands between Paci- 

 lasma and Megalasma^ and doubtless was ancestral to the latter genus, 

 which difi'ers from Glyptelasma only by the rotation of the basal mar- 

 gin of the scutum through 90°, bringing it in line with the occhident 

 margin. The apparent change in the position of the umbo is due to 

 this rotation. Morphologically its position is the same in Megalasma^ 

 Patcilas'ma., and Lepas. 



The characters of the groups under discussion are exhibited in the 

 following analytical key. 



KEY TO GENERA AND SUBGENERA. 



a. Carina expanded around and below the umbo in a flat, rounded di.sk, the upper 



end acute; no terga; upper margin of scutum rounded Tr'da&mh. 



aa. Carina with basal, 'terminal umbo, the upper end obtuse; terga present. 



h. Carina narrow throughout, not expanding laterally at the base; surface 

 of the valves smoothish. 



« Bulletin of the Bureau of Fisheries, XXVI, 1907, p. 183. 



