THE BARNACLES IN THE U. S. NATIONAL MUSEUM. 



83 



c. Scutum not slit; cirri normal Precilasma. 



cc. Scutum usually divided by an arcuate slit; cirri peculiar Temnaspis. 



bb. Carina with wide sides, expanding laterally in the lower part or at the base; 

 scutum biangular above, with a distinct ridge to tergo-carinal angle; sur- 

 face roughened, 

 c. Basal or peduncular margin of scutum making a right angle with the 



occludent margin, the umbo at the angle Gbjptelasrnu. 



cc. Basal or peduncular margin of scutum a continuation of the occludent mar- 

 gin, the umbo therefore above the basal angle of the plate. ..Megalasma. 



The 'relations of the groups are expressed in the following' diagram: 



Trilasmis 

 Temnaspis 

 Octolasmis Pteci 



Megalasma 



M. bellum 

 asma Glyptelasraa 



Pentaspidian 

 ancestor. 



I have examined the mouth parts and cirri in Psecilasma Jcsempferi^ 

 P. k. littan^ P. incBquilaterale^ Megalasmia annandalei, and M. gracilius. 

 There is an unusual uniformity throughout these forms. The arma- 

 ture of the cirri reminds one of Scal^pellwn. 



KEY TO AMERICAN SPECIES OF PCECILASMA AND MEGALASMA. 



a. Carina wide in its lower part, expanding laterally near the base. 



b. Basal margin of the scutum about at a right angle with the occludent margin. 

 East American. 

 c. Umbo of carina projecting beak-like below the base of the scutum, and at an 

 angle with it. 

 d. Basal margin of carina as long as the base of the scutum, its sides wide in 



the lower half M. g. gracilius. 



dd. Basal margin of carina shorter than base of scutum, its sides wide in the 



lower third M. annandalei. 



cc. Uml)0 of carina not produced below base of scutum. 



d. Occludent margin nearly straight; carina with the basal margin straight, 



the sides-narrow, abruptly auriculate at base J/, reel ton. 



dd. Occludent margin well arched ; carina with very wide sides, the basal margin 



as long as that of the scutum }[. subcm-inatuin. 



bb. Basal margins of the scutum and carina nearly parallel to the occludent margin; 



sides of carina very wide. Hawaiian 3L bellunt . 



au. Carina narrow throughout, not expanding laterally at the base. 



b. Carinal end of the terguni very short P. innquilaterule_ 



bb. Carinal end of the tergum longer, about half as long as the occludent margin. 

 <■. A distinct ridge or angle extending from umb > to tergo-carinal angle of 

 scutum; basal margin of scutum less than half the length of the ter- 

 gum P. kiempferi novseanglix. 



cc. No distinct ridge to the tergo-carinal angle of scutum. 



