516 LAGANIDAE. 



LAGANIDAE. 



Subfamily Laganidae Des., 1857, Synops., 217. (emend.) 



In this subfamily the connection between the two floors is made by walls 

 running parallel to the edge of the test; well-developed buccal tubes; 

 petals lanceolate; interambulacra extremely narrow on the actinal side of 

 the test ; ambulacra! furrows straight, and outline more or less pentagonal. 



LAGANUM. 



Laganum Klein, 1734, Nat. Disp. Ech. 



Echini of large and medium size, with depressed test, subpentagonal, often 

 with swollen edge Ambulaeral petals lanceolate, closed before reaching the 

 margin, scarcely extending beyond half-way between the apex and the 

 margin of the test. Pores distinctly conjugated. Interambulacra narrow, es- 

 pecially upon the lower side, which is flat, with simple, broad, shallow, porous 

 ambulacra running a short distance beyond the peristomal star, but not 

 reaching the margin. Supports of the edge concentric with it. broad, and 

 few in number ; not more than two to three parallel rows of walls. The 

 primary tubercles are uniformly scattered over the surface, and much less 

 numerous than in the other Scutellae. The miliaries are more numerous. 

 The teeth articulated upon a groove in the upper surface of jaws ; the tip 

 of the teeth alone is enamelled, and. although massive, the jaws are not quite 

 built upon the pattern of the Clypeastroids, hut are never like the jaws of 

 Scutellidae. Anus infra-marginal. The outline is more or less pentagonal, 

 angular or rounded anteriorly, and truncated posteriorly. 



There are no pillars usually between the jaws and the alimentary canal ; 

 five genital openings; the upper and lower Hours are perfectly smooth : the 

 sutures of the plates of the petals are well seen from the interior. Several 

 of the species of Laganum have a superficial resemblance to the Hat Cly- 

 peastri ; this has led to considerable confusion between the species of the 

 two genera with Clypeaster seutiformis and Clypeaster humilis. 



