NOETH AMEEICAN STAEFISHES. 97 



corresponding interbracliial partition of A. berylinus, and also PI. XI. Fir/. 4, 

 the prolongation of the plates separating adjoining ambulacral systems 

 in A. ochracea and in A. berylinus (PI. IX. Fir/. 5). To show the differ- 

 ence in the thickness of the limestone reticulation of the abactinal and 

 actinal systems compare PI. XL Fig. 3, and PI. IX. Fig. 4, which are simi- 

 lar views of the interior of the abactinal systems of A. berylinus and A. 

 ochracea. or compare the horizontal sections shown in PI. XI. Fig. 5, and 

 PI. IX. Fig. 6. The range of Asterias ochracea is from Sitka to San 

 Diego, California ; it is the most common species of Starfish on the coast 

 of California. 



Echinaster sentus. 



Asleiias sentus Say, 1825. Journ. Acad. Nat. Scien. Phila., V. 143. 

 Echinaster sentus Verr. 1867. Notes on Radiata. 



Fl X. 



The meshes of the abactinal limestone network are larger than in 

 Asteracanthion, especially near the centre of the disk, where the irregu- 

 lar polygonal spaces covered by the abactinal membrane are quite large 

 (PI. X. Fig. 3). The same loose structure extends a short distance along 

 the abactinal surface (PI. X. Fig. 4) and the sides of the arms ; but 

 towards the extremity the meshes become smaller, and on the actinal 

 side, immediately adjoining the interambulacral plates, the limestone work 

 is quite compact (PI. X. Figs. 5, 6), and leaves only a few small openings 

 for the passage of the water-tubes. 



In addition to the water-tubes in the actinal surface of the arms, 

 there is a row of very large tubes (PI. X. Fig. 1') passing between the 

 interambulacral plates. The madreporic body differs considerably from 

 that of Asteracanthion, and is not as well separated or as distinct from 

 the general abactinal surface as is the case in that genus. 



The interambulacral plates, forming the so-called teeth, are larger than 

 the others ; they form the extremity of the single lateral rows (PI. X. Fig. 

 5), and do not make a partition or division-wall between adjoining am- 

 bulacra, as in Asteracanthion proper, the actinal part of the limestone net- 

 work extending nearer the actinostome. The solid character of the 

 actinal part of the limestone network covering the arms is well shown 

 in an interior view (PI. X. Fig. 6). This figure also shows how far the 

 ambulacral and interambulacral plates become soldei'ed together with the 



