ASTROPYGA PULVINATA. 419 



owing to great breadth of the bare interambulacral space, the test is quite 

 bare, the tubercles more irregular in size : it is not the exterior primary 

 row of tubercles which reaches the abactinal system, but the next inner 

 row of secondaries ; in younger specimens, however, the reverse is the case. 

 A small specimen, figured on Plate IIP, was remarkable for the great con- 

 vexity of the edge of test, and the -uniformly flattened abactinal part of the 

 test ; ambulacra rising but slightly above the median interambulacra. 



The great size of the actinostome of this species readily distinguishes it 

 from A. radiata, in A. pulvinata the actinostome being nearly a third of the 

 diameter of the test. The vertical rows of primary tubercles of ambulacra 

 are distant, frequently only every other plate carrying a primary, the oppo- 

 site being only a secondary tubercle. In this species, as in radiata, the spots 

 on the pits of the interambulacra (which are much less marked than in A. 

 radiata) are also sky-blue in life, according to Mr. Bradleigh : the color in 

 alcohol is yellowish below ; above, the ambulacra are more greenish-yellow 

 between the broad purple bare interambulacral spaces. The spines are com- 

 paratively longer than in A. radiata, in addition to being so much stouter, 

 often considerably more than half the diameter of the test, scarcely ever 

 longer than half the diameter in A. radiata, usually only one third ; they are 

 flesh-colored, with brownish-purple transverse bands. The dried test is of a 

 dirty greenish-white hue, much lighter below ; the median interambulacral 

 space between the bare forks above the ambitus being as light as the actinal 

 part of test, The comparatively narrower ambulacral zone in the abactinal 

 part of the test is quite marked in A. pulvinata when compared to A. 

 radiata. 



In the large specimens in the Jardin des Plantes of A. pulvinata the ratio 

 of actinostome to diameter of test was T 3 7 , while it was T 3 ¥ 4 7 in A. radiata. 



The discovery of the habitat of this species is quite interesting, render- 

 it possible to trace precisely the geographical distribution of the two species 

 of the genus, concerning both of which many doubts existed. Mr. Brad- 

 leigh found this species at Panama ; and it had previously been received 

 at the Smithsonian from San Salvador, and at the Hamburg and Stockholm 

 Museums from the Gulf of California, settling its geographical position be- 

 yond doubt. 



Panama ; Gulf of California. 



