5G2 HOMOLAMPAS. 



HOMOLAMPAS. 



Lissonohm (A. Ag.), 18G9, Bull. M. C. Z., I. (non Schonh.) 

 Homolampas A. Ag., 1872, Rev. EcL, Pt. I., p. 137. 

 (Scl- Part II. p. 34 7.) 



Homolampas fragilis 



! Lissonotus fragilis A. Ac, 1869, Pull. M. C. Z., I. p. 273. 

 ! Homolampas fragilis A. Ac, 1872, Rev. Ech., Pt, I. p. 137. 

 (See Part II. p. 348.) 



PI. XVII. f. 13-21. 

 Straits of Florida. 



PLATYBRISSUS. 



Platybrissus Grtjbe, 18G5, Jahresb. d. Sollies. Ges. f. Vat Cult. 



This genus forms the connecting link between the Spatangina, such as 

 Spatangus proper, and genera closely allied to the Ananchytidae. The test 

 is depressed (in the only species known); outline regularly elliptical ; pos- 

 terior extremity rounded ; anal system placed in the uniformly swollen edge 

 of the test. Ambulacra flush with the test, terminating abruptly at the ex- 

 tremity ; poriferous zones nearly parallel ; pores not conjugate. Actinostome 

 large, with the edge forming an irregular polygon with a broad side at the 

 posterior ed-v ; anterior lip slightly sunken, so that the aetinal opening is 

 nearly on one level, much as we find it in Eupatagus, which genus Platy- 

 luissus strikingly recalls at first glance, though structurally so different, 

 Aetinal plastron small, not independent, reduced to a narrow point, ex- 

 tending a short distance in the broad bare aetinal avenue, formed by 

 the coalescence of the adjoining posterior ambulacra! spaces. The total ab- 

 sence of fascioles of any kind, either peripetalous, anal, or subanal, is a 

 remarkable feature possessed by many cretaceous Spatangoids ; but it is 

 the first case recorded of such a structure in any of the recent species. 

 The tuberculation of the aetinal surface is large, distant, with few small 

 miliaries irregularly scattered ; the largest tubercles are placed on the very 

 edge of the bare aetinal avenue, and near the actinostome ; that of the 

 abactinal surface is similar, but with secondary as well as miliary tubercles, 

 decreasing in size towards the apex. 



