more specialized subgroups of Chilomycterus (the af- 

 finis, atinga, reticulatus, (igrinuA- subgroup, and the or- 

 bicularis subgroup) they differ from the more generalized 

 subgroup of Chilomycterus {antennatus, antillarum, 

 mauretanicus, schoepfi, spinosus) only slightly, pri- 

 marily by retaining at least some erectile spines without 

 huge triradiate bases. 



Relationship to the other Tetraodontoidei.— The 



relationship of the Diodontidae as a specialized offshoot 

 of the line of gymnodonts leading to the Tetraodontidae 

 is discussed under the latter and under the Trio- 

 dontidae, with additional remarks under the Molidae. 



SUPERFAMILY MOLOIDEA 



Comparative diagnosis (contrast with that of the 

 Tetraodontoidea), which is also that of its only con- 

 tained family, the Molidae.— No inflatable diver- 

 ticulum of the gut; first branchiostegal ray without an 

 inturned and enlarged dorsal edge, articulated to the 

 ventral edge of the ceratohyal and not forming a pump- 

 ing plate; air bladder absent, at least in adults; four gills, 

 greatly expanded dorsally above and beyond the sup- 

 porting arches; a gill slit present between the gill bearing 

 fourth arch and the gill-less fifth arch, with gill rakers 

 present along both the posterior edge of the fourth arch 

 and the anterior edge of the fifth arch; gill rakers present 

 along the anterior edge of the first gill slit; pharyngo- 

 branchials with extremely large teeth, the three ele- 

 ments being those of the second to fourth arches; cera- 

 tohyal and epihyal not sutured to one another; interhyal 

 and dorsal hypohyal always present; teeth in biting edge 

 of jaws apparently indistinguishably incorporated into 

 the bony matrix of the preraaxillary and dentary; 

 basisphenoid present; caudal fin aborted, either absent 

 altogether or represented by only a few rays in the cen- 

 tral region of the pseudocaudal fin formed by posteriorly 

 migrated soft dorsal and anal fin rays and supported 

 mostly by equally posteriorly migrated basal pterygio- 

 phores from the soft dorsal and anal fins; dorsal, anal, 

 caudal, and pectoral fin rays often extensively branched 

 but with extremely few cross-striations, those present 

 only at the extreme distal ends of the rays; sesamoid ar- 

 ticular absent; postcleithrum with an anteriorly di- 

 rected process toward or over the actinosts; three acti- 

 nosts; supracleithrum extremely elongate, broadly ar- 

 ticulated over the anterior one-third to one-half of its 

 length with the pterotic; coracoid long and slender, 

 without a posterodorsal prong below the lower actinost; 

 operculum and suboperculum of greatly simplified struc- 

 ture and reduced lateral surface area; interoperculum 

 absent as an ossification or present as a simple slender 

 rod of bone not extending posteriorly beyond the level of 

 the epihyal; basioccipital greatly prolonged dorsally 

 behind the exoccipitals to border the foramen magnum 

 to the exclusion of the exoccipitals; exoccipitals without 



Figure 304.— Range of diversity in body 



form in the Molidae: Mola mola (left) 



and Romania laevis (right). 



condyles and not in contact with the first vertebra, which 

 articulates anteriorly only with the basioccipital; epiotic 

 with a high dome or ribbonlike posterodorsal prolonga- 

 tion; pterotic greatly prolonged posteriorly, well past the 

 level of the end of the basioccipital; bony canal for the 

 nerves and blood vessels running from the orbit to the 

 nasal region complete, entirely surrounded by the pre- 

 frontal; palatine receiving its main support dorsally by a 

 broad articulation with the ethmoid, vomer (if present), 

 prefrontal, and parasphenoid; no vertebrae with bifid 

 neural spines projecting dorsally or dorsolaterally on 

 each side of the neural arch; centra of the abdominal 

 vertebrae without any ventral or ventrolateral processes, 

 the ventral and ventrolateral surfaces of the centra 

 perfectly smooth; dorsal and anal fin rays widely 

 separated from their basal pterygial supports by a large 

 block of cartilage; scales small but the basal plates in 

 more or less close contact and forming a continuous 

 covering over the entire body, with none of the scales in 

 the form of prominent prickles or spines; two minute 

 nostrils flush with the surface of the skin; lateral line 

 either absent or extremely inconspicuous (not discerni- 

 ble to me on either cleared and stained or intact alcohol 

 preserved specimens at 30 magnifications). 



Detailed description of Mola mola. 



Material examined. — Two cleared and stained speci- 

 mens, 306 mm and 310 mm; two sets of jaws from large 

 specimens of unknown length, one dry and one alcohol 

 preserved. 



Occipital Region. 



Basioccipital. — A short column, expanded at the 

 anterior end and prolonged anterodorsally into a pair of 

 sturdy prongs much like those of the first vertebra; 

 broadly cartilage filled along the expanded anterior edge 



