~ 



44 PALEONTOLOGY. 



those in the quartz rocks of Sutherland are thicker in propor- 

 tion. The Microconchus of the carboniferous period is now re- 

 garded as an Anellide ; and in all the later formations, tubicolar 

 Anellides, especially of the genera Serpula, Spirorbis, and Ver- 

 milia abound. Some of these, although attached and gregarious, 

 are so regular in their growth as to have been usually called 

 Vermeti, but are now placed in the genus Vermicularia. 

 Spiroglyjphus, and some other shell-excavators, are indicated 

 in the tertiaries. Amongst the problematic fossils of the 

 palaeozoic strata, two are supposed to be anellidous, viz., the 

 Tentaculites (fig. 10, 7)- which was apparently free, and almost 

 always regular in its growth, so as more to resemble one of the 

 gregarious Pteropods ; and the Comulite (fig. 10, 8), which is 

 attached when young, singly or in groups, to Silurian shells 

 and corals : the structure of its shell is vesicular, and the 

 cavity resembles a series of inverted cones. The unattached 

 and gregarious. Ditrupa appears in the upper chalk, and 

 abounds in the London clay and crag. r 



Class II.— CIKK1PEDIA. 



(Barnacles, Acorn- Shells). 



Char. — Body chitinous or chitino-testaceous, subarticulated, 

 mostly symmetrical, with aborted antennae and eyes ; 

 thorax attached to the sternal surface of the carapace, 

 with six pairs of multiarticulate, biramous, setigerous, 

 limbs ; metamorphosis resulting in a permanent para- 

 sitic attachment of the fully-developed female to some 

 foreign body. 



The fossil Cirripedes belong chiefly to the sessile division, 

 and consist of the ordinary forms of the still-existing Balanidce. 

 They are rare in the eocene tertiary, but more abundant after- 

 wards. The Balanus porcatus attains a great size in the shelly 

 beds of northern drift ; its large basal plate, when detached, 



