62 SVEN LOVEN, ECHINOLOGICA. 



in fi(). 50, tlie nwi. re. 2 alone are to be seen. Eacli m. re. 1 

 is tliin, of a somewliat rhomboidal shape, and is attached to 

 the lower lialf or two tliirds of tlie margin of tlie furrow on 

 tlie inner börder of tlie anricle, whence it extends horizontally 

 and adorally Avhile it gradiially thickens and becomes convo- 

 lute, fuj. 54, 55; both m. re. 1. are inserted on either side of 

 the septum, fig. 58, in two diverging, liooked impressions. 



Of the »I. re. 2, the aboral parts of the retraotors, each 

 is attached to the auricle in horse-shoe form close under the 

 crest of its top. They are rather thick at the origin and thin 

 oflp downAvards, closely contiguous to the m. re. 1 and sprea- 

 ding triangularly, and liave their very narrow lines of inser- 

 tion on either side of the septum abutting to those of the m. 

 re. 1 at their aboral ends, fig. 53, 54, 55, 56, 58. 



The protractors, m. pro., fig. 58, 54, 56, are two small 

 muscles attached to the inner surface of the test, interradially, 

 but on the expanded base of the auricles. They ascend, flatte- 

 ning and broadeniug, and insert themselves on the crest of 

 the sejjtum, betvveen the m. re. 2 in two short linear impres- 

 sions, fig. 58. 



Of the alveolar Avall of the pyramid the compacted tissue 

 does not occupy as broad a central part as in the Regularia, 

 and there is no central canal. The two »linese eminentes», 

 therefore, are contiguous at the symphysis, P/. X, fig. 131, 

 132. Above, they terminate with two points, representing the 

 styloid processes of the Regularia, but sessile. The dull, rougli 

 area of each linea, x , extends with all but the same breadth 

 through nearly two thirds of the length, and then gradually 

 contracts to half its breadth near the lips, fig. 132. 



As in the Regularia the tooth is composed of two distinct 

 parts, the lameilar bod}^ the »Zahnkörper of Giesbrecht,^ 

 which is applied to the slide, and the prismal part, which in 

 the Echinidse forms the keel, the carina Val., that stånds 

 ont into the cavity, and in the CidaridjE lines the hollow of its 

 adoral groove, the petrous portion of the body being in both 

 produced, beyond the more friable part, into the pointed apex. 

 In Clypeaster, fig. 131, the keel is much longer in proportion 

 to the body of which its basis occupies nearly the entire 

 breadth, and forms the main mäss of the tooth, which is very high, 



' 1. c. p. il. 



