1915.] NATURAL SCIENCES OF PHILADELPHIA. 59 



Subfamily 2. ASTROTOMINiE nov. 



(Characters as given in keys, p. 55.) 



This subfamily includes Astrothrombus, Astrothorax, Astrotoma 

 and Astroclon, besides a new genus, Astrothamnus. 



Astrothamnus gen. nov. 



Disk divided into ten radiating lobes by radial and interradial 

 furrows, closely covered with coarse granules or stumpy tubercles, 

 which are acute or thorny at tips. Ventral interradial areas strongly 

 concave, with large, long, more or less parallel genital slits. Teeth 

 and dental papillae similar, spiniform, forming a cluster at the apex 

 of each jaw. Oral papillae absent, so that the sides of the oral slits 

 are naked. Arms simple, distinctly annulated by zones of densely 

 set, minute, compound hooks; the interannuli are covered with 

 coarse granules, which are arranged more or less clearly in two 

 series. Arm spines 3-5, peg-like, usually rough at tips, serving as 

 tentacle scales. 



This genus includes Koehler's Astrotoma hellator, A. vecors and A. 

 rigens, besides the genotype, Astrothamnus ecJmiaceus sp. nov. 



Astrothamnus is distinguished from genuine Astrotoma as follows: 



A — Disk covered with coarse granules or stumpy tubercles, which 

 are acute or thorny at tip; arms annulated by conspicuous 

 zones of densely set compound hooks; interannuli of arms 

 covered with coarse granules, which are arranged more or less 

 clearly in two series Astrothamnus. 



AA — Disk covered with very fine, smooth granules, often beset 

 with a number of smooth, stumpy tubercles; arms rather 

 inconspicuously annulated, each annulus consisting of four 

 rows of granules, the middle two hook-bearing, while the 

 others are smooth; interannuli covered by a pavement of 

 very fine granules, among which many oval, sunken plates 

 are present Astrotoma, restr. 



In the arm coverings, Astrothamnus is similar to Astrothrombus 

 and Astrothorax, while Astrotojna, restr., resembles Astroclon. Thus 

 the Astrotominae fall naturally into two groups, one of which includes 

 the first three genera, and the other the last two. 



Astrothamnus echinaceus (Matsumoto). 



Astrotoma echinacea, 1912. Dobuts. Z. Tokyo, 24, p. 200 (in Japanese); 

 figs. 6-8. 



Diameter of disk, 22 mm. Length of arms, 140 mm. Width of 

 arms at base, 4 mm. Disk distinctly five-lobed by five interradial 

 furrows, each lobe being again divided into two secondary lobes by 



