584 MOLLUSCA SUB-KINGDOM VI 
Family 20. Spiroceratidae. Phylogerontic, uncoiled, and straight forms, 
probably derived from some of the preceding family. Young are attenuated cones 
with single straight costae, but have four rows of tubercles at an early stage and a 
concave zone along the venter. 
Sutures of Reineckian type, but 
reduced to the phylogerontie formula 
of six lobes. 
Sptroceras, Quenst. (Fig. 1222) ; 
Apsorroceras, gen. nov. Type A. 
(Ham.) baculatus, Quenst. sp. In- 
ferior Oolite. Incertae sedis: 
Baculina, VOrb. Oxfordian and 
Neocomian. 
Family 21. Hoplitidae. Dis- 
coidal and involute forms with costae 
bifurcated on the sides at umbilical 















Fic. 1222. Fic. 1223. 
Spiroceras bifurcatum, Quenst. sp. Upper Dogger (Cal- Hoplites_tuberculatus, Sowb. sp. 
lovian); Ehningen, Wiirtemberg. A, Shell with protoconch Gault; Folkestone, England. 
broken away, 1/;. LB, Portion of venter. C, Suture-line. Siphuncle broken away. 
shoulders; prominent tubercles at their forks, and also at or near their ventral 
termini, these last being separated by a median zone or deep channel. Young of 
some species have costae continuous across the venter, and resemble those of Sonneratia. 
Parallelism with Cosmoceratidae very close. Sutures resemble those of Mammitidae, 
but more complex. Lateral saddles narrower and more deeply cut, and first lateral 
saddles often trifid in late stages. Dorsal series with two pairs of complex zygous 
lobes and saddles on either side of a long, narrow, complex, antisiphonal lobe. 
Hoplites, Neum. (Fig. 1223); Cenomanites, Haug (Discoceras, Kossmat); Son- 
neratia, Bayle; Anahoplites, gen. nov. Type <A. (Amm.) splendens, VOrb. sp. 
Cretaceous. 
VILI. PLACENTICERATIDA. 
Young, smooth, and compressed, with flat or concave venter, which may subsequently 
become acute, or remain flat throughout life, or may even become keeled. Outline apt to be 
rounded in old age; sides may have as many as three rows of tubercles, but in most 
forms are not highly ornamented. Sutures remarkably complex in some families, but in 
others extremely simple, recalling those of Triassic genera. General tendency is to extend 

