SUMMARY. 



177 



trigeminal. Oral opening variable in size. Peristome more or less decagonal, deeply or 

 feebly notched. Jaws present. Apical disc usually greatly developed, with an additional 

 suranal shield, sometimes formed of one piece, sometimes of from three to eight pieces. 

 Spines long and slender, covered with fine longitudinal strife. Range of family from the 

 Lias to the existing period. One British Liassic and Oolitic genus, AcROSAiiENiA, with 

 ten British species. 



Genus 13. — Acrosalenia, Agassiz (Vol. I, p. 229). 



Test thin, spheroidal or depressed. Ambulacral areas narrow, straight, or slightly 

 undulated, with two rows of small crenulated and perforated tubercles on their margins. 

 Interambulacral tubercles perforated, raised on large prominent bosses, with crenulated 

 summits. Jaws present. Apical disc moderately small and not prominent. Sur-anal shield 

 composed of one or many pieces. Anal opening slightly excentric. Range of the genus 

 from the Lias to Lower Cretaceous. Ten British Liassic and Oolitic species (Vol. I, 

 pp. 230—249, 460—462). 



Section B.— Echinoidea exocyclica, Wrlcjhi (Vol. I, p. 17). 



Anal opening outside the genital plates, never opposite the mouth. 



The section contains eight families, Echinoconidse, Collyritidse, Echinonidae, 

 Echinobrissidse, Echinolampidse, Clypeasteridse, Echinocoridae, Spatangidce, and ranges 

 from the Lias to the existing period. Eour families (Echinooonid^, CoLLTRiTiD.a;, 

 EcHiNOBRissiDiE, and EcHiNOLAMPiD^) are represented in the British Liassic and Oolitic 

 strata by eight genera: Holectypus, Pygaster, Hyboclypus, Galeropygus, Colly- 

 rites, EcHiNOBuissus, Clypeus, Pygurus ; and by thirty-eight species. 



Family VL— ECHINOCONID^, Wright (Vol. I, p. 258). 



Test thin, circumference circular or subpentagonal. Upper surface conical ; under 

 surface somewhat flat. Ambulacral areas narrow, simple, and lanceolate. Interambulacral 

 wide, bearing small perforated tubercles, arranged more or less regularly, and supported on 

 bosses with smooth or crenulated summits. Poriferous zones continuous from oral 

 opening to apical disc ; pores unigeminal, except near the mouth, where they are in 

 triple oblique pairs. Oral opening circular, central, or subcentral. Peristome more or 

 less divided by notches into ten lobes. Jaws present. Anal opening large and excentrical, 

 oblong, dorsal, marginal, infra-marginal, or basal, sometimes occupying the entire space 

 from the mouth to the border. Apical disc, mostly central and vertical, with five 



